Video decoding method using simplified residual data coding in video coding system, and apparatus therefor

ABSTRACT

A method for performing video decoding by a decoding device according to the present document comprises the steps of: acquiring residual information of a current block; deriving residual samples of the current block on the basis of the residual information; and generating a reconstructed picture on the basis of the residual samples.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure relates to an image coding technique and, moreparticularly, to an image coding method and an apparatus therefor, incoding residual data according to TSRC of a current block in an imagecoding system, in the case that all maximum available context-coded binsfor the current block are used, for coding the subsequent residual dataaccording to a simplified residual data coding structure.

Related Art

Recently, demand for high-resolution, high-quality images, such as HighDefinition (HD) images and Ultra High Definition (UHD) images, has beenincreasing in various fields. As the image data has high resolution andhigh quality, the amount of information or bits to be transmittedincreases relative to the legacy image data. Therefore, when image datais transmitted using a medium such as a conventional wired/wirelessbroadband line or image data is stored using an existing storage medium,the transmission cost and the storage cost thereof are increased.

Accordingly, there is a need for a highly efficient image compressiontechnique for effectively transmitting, storing, and reproducinginformation of high-resolution and high-quality images.

SUMMARY

The present disclosure provides a method and apparatus for improvingimage coding efficiency.

The present disclosure also provides a method and apparatus forimproving residual coding efficiency.

According to an embodiment of this document, an image decoding methodperformed by a decoding apparatus is provided. The method includesobtaining residual information of a current block, deriving residualsamples of the current block based on the residual information, andgenerating a reconstructed picture based on the residual samples.

According to another embodiment of this document, a decoding apparatusperforming image decoding is provided. The decoding apparatus includesan entropy decoder configured to obtain residual information of acurrent block, a residual processor configured to derive residualsamples of the current block based on the residual information, and anadder configured to generate a reconstructed picture based on theresidual samples.

According to still another embodiment of this document, an imageencoding method performed by an encoding apparatus is provided. Themethod includes deriving residual samples for a current block,generating residual information for the residual samples, and encodingimage information including the residual information.

According to still another embodiment of this document, an imageencoding apparatus is provided. The encoding apparatus includes aresidual processor configured to derive residual samples for a currentblock and an entropy encoder configured to generate residual informationfor the residual samples and encode image information including theresidual information.

According to still another embodiment of this document, a non-transitorycomputer-readable storage medium storing a bitstream including imageinformation causing an image decoding method to be performed isprovided. In the non-transitory computer-readable storage medium, theimage decoding method includes obtaining residual information of acurrent block, deriving residual samples of the current block based onthe residual information, and generating a reconstructed picture basedon the residual samples.

According to the present disclosure, the efficiency of residual codingmay be improved.

According to the present disclosure, when the maximum number ofcontext-coded bins for a current block is consumed in TSRC, syntaxelements according to a simplified residual data coding structure may besignaled, and through this, the coding complexity of bypass-coded syntaxelements is reduced, and the overall residual coding efficiency may beimproved.

According to the present disclosure, as a coding order of bypass-codedsyntax elements, an order in which a syntax element is preferential maybe used, and through this, the coding efficiency of the bypass-codedsyntax elements may be improved, and the overall residual codingefficiency may be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 briefly illustrates an example of a video/image coding device towhich embodiments of the present disclosure are applicable.

FIG. 2 is a schematic diagram illustrating a configuration of avideo/image encoding apparatus to which the embodiment(s) of the presentdisclosure may be applied.

FIG. 3 is a schematic diagram illustrating a configuration of avideo/image decoding apparatus to which the embodiment(s) of the presentdisclosure may be applied.

FIG. 4 illustrates an example of an inter prediction-based video/imageencoding method.

FIG. 5 illustrates an example of an inter prediction-based video/imagedecoding method.

FIG. 6 schematically shows an inter prediction procedure.

FIG. 7 exemplarily shows context-adaptive binary arithmetic coding(CABAC) for encoding a syntax element.

FIG. 8 is a diagram showing exemplary transform coefficients within a4×4 block.

FIG. 9 illustrates an example in which the syntax elements are coded inTSRC.

FIG. 10 illustrates another example in which the syntax elements arecoded in TSRC.

FIG. 11 illustrates another example in which the syntax elements arecoded in TSRC.

FIG. 12 illustrates an example of coding syntax elements bypass-coded inTSRC in a coding order in which a syntax element is preferential insteadof a coding order in which a coefficient position is preferential.

FIG. 13 illustrates an example of coding syntax elements bypass-coded inTSRC in a coding order in which a syntax element is preferential insteadof a coding order in which a coefficient position is preferential.

FIG. 14 illustrates an example in which syntax elements are coded in thesimplified residual data coding structure.

FIG. 15 illustrates an example of coding syntax elements bypass-coded inthe simplified residual data coding structure in a coding order in whicha syntax element is preferential instead of a coding order in which acoefficient position is preferential.

FIGS. 16a and 16b illustrate embodiments in which syntax elements arecoded in the simplified residual data coding structure.

FIGS. 17a and 17b illustrate an example of coding syntax elementsbypass-coded in the simplified residual data coding structure in acoding order in which a syntax element is preferential instead of acoding order in which a coefficient position is preferential.

FIG. 18 illustrates embodiments in which syntax elements are coded inthe simplified residual data coding structure.

FIG. 19 illustrates an example of coding syntax elements bypass-coded inthe simplified residual data coding structure in a coding order in whicha syntax element is preferential instead of a coding order in which acoefficient position is preferential.

FIG. 20 briefly illustrates an image encoding method performed by anencoding apparatus according to the present disclosure.

FIG. 21 briefly illustrates an encoding apparatus for performing animage encoding method according to the present disclosure.

FIG. 22 briefly illustrates an image decoding method performed by adecoding apparatus according to the present disclosure.

FIG. 23 briefly illustrates a decoding apparatus for performing an imagedecoding method according to the present disclosure.

FIG. 24 illustrates a structural diagram of a contents streaming systemto which the present disclosure is applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present disclosure may be modified in various forms, and specificembodiments thereof will be described and illustrated in the drawings.However, the embodiments are not intended for limiting the disclosure.The terms used in the following description are used to merely describespecific embodiments but are not intended to limit the disclosure. Anexpression of a singular number includes an expression of the pluralnumber, so long as it is clearly read differently. The terms such as“include” and “have” are intended to indicate that features, numbers,steps, operations, elements, components, or combinations thereof used inthe following description exist and it should be thus understood thatthe possibility of existence or addition of one or more differentfeatures, numbers, steps, operations, elements, components, orcombinations thereof is not excluded.

Meanwhile, elements in the drawings described in the disclosure areindependently drawn for the purpose of convenience for explanation ofdifferent specific functions, and do not mean that the elements areembodied by independent hardware or independent software. For example,two or more elements of the elements may be combined to form a singleelement, or one element may be partitioned into plural elements. Theembodiments in which the elements are combined and/or partitioned belongto the disclosure without departing from the concept of the disclosure.

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings. In addition, likereference numerals are used to indicate like elements throughout thedrawings, and the same descriptions on the like elements will beomitted.

FIG. 1 briefly illustrates an example of a video/image coding device towhich embodiments of the present disclosure are applicable.

Referring to FIG. 1, a video/image coding system may include a firstdevice (source device) and a second device (receiving device). Thesource device may deliver encoded video/image information or data in theform of a file or streaming to the receiving device via a digitalstorage medium or network.

The source device may include a video source, an encoding apparatus, anda transmitter. The receiving device may include a receiver, a decodingapparatus, and a renderer. The encoding apparatus may be called avideo/image encoding apparatus, and the decoding apparatus may be calleda video/image decoding apparatus. The transmitter may be included in theencoding apparatus. The receiver may be included in the decodingapparatus. The renderer may include a display, and the display may beconfigured as a separate device or an external component.

The video source may acquire video/image through a process of capturing,synthesizing, or generating the video/image. The video source mayinclude a video/image capture device and/or a video/image generatingdevice. The video/image capture device may include, for example, one ormore cameras, video/image archives including previously capturedvideo/images, and the like. The video/image generating device mayinclude, for example, computers, tablets and smartphones, and may(electronically) generate video/images. For example, a virtualvideo/image may be generated through a computer or the like. In thiscase, the video/image capturing process may be replaced by a process ofgenerating related data.

The encoding apparatus may encode input image/image. The encodingapparatus may perform a series of procedures such as prediction,transform, and quantization for compression and coding efficiency. Theencoded data (encoded video/image information) may be output in the formof a bit stream.

The transmitter may transmit the encoded image/image information or dataoutput in the form of a bit stream to the receiver of the receivingdevice through a digital storage medium or a network in the form of afile or streaming. The digital storage medium may include variousstorage mediums such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and thelike. The transmitter may include an element for generating a media filethrough a predetermined file format and may include an element fortransmission through a broadcast/communication network. The receiver mayreceive/extract the bit stream and transmit the received bit stream tothe decoding apparatus.

The decoding apparatus may decode the video/image by performing a seriesof procedures such as dequantization, inverse transform, and predictioncorresponding to the operation of the encoding apparatus.

The renderer may render the decoded video/image. The renderedvideo/image may be displayed through the display.

Present disclosure relates to video/image coding. For example, themethods/embodiments disclosed in the present disclosure may be appliedto a method disclosed in the versatile video coding (VVC), the EVC(essential video coding) standard, the AOMedia Video 1 (AV1) standard,the 2nd generation of audio video coding standard (AVS2), or the nextgeneration video/image coding standard (e.g., H.267 or H.268, etc.).

Present disclosure presents various embodiments of video/image coding,and the embodiments may be performed in combination with each otherunless otherwise mentioned.

In the present disclosure, video may refer to a series of images overtime. Picture generally refers to a unit representing one image in aspecific time zone, and a subpicture/slice/tile is a unit constitutingpart of a picture in coding. The subpicture/slice/tile may include oneor more coding tree units (CTUs). One picture may consist of one or moresubpictures/slices/tiles. One picture may consist of one or more tilegroups. One tile group may include one or more tiles. A brick mayrepresent a rectangular region of CTU rows within a tile in a picture. Atile may be partitioned into multiple bricks, each of which consistingof one or more CTU rows within the tile. A tile that is not partitionedinto multiple bricks may be also referred to as a brick. A brick scan isa specific sequential ordering of CTUs partitioning a picture in whichthe CTUs are ordered consecutively in CTU raster scan in a brick, brickswithin a tile are ordered consecutively in a raster scan of the bricksof the tile, and tiles in a picture are ordered consecutively in araster scan of the tiles of the picture. In addition, a subpicture mayrepresent a rectangular region of one or more slices within a picture.That is, a subpicture contains one or more slices that collectivelycover a rectangular region of a picture. A tile is a rectangular regionof CTUs within a particular tile column and a particular tile row in apicture. The tile column is a rectangular region of CTUs having a heightequal to the height of the picture and a width specified by syntaxelements in the picture parameter set. The tile row is a rectangularregion of CTUs having a height specified by syntax elements in thepicture parameter set and a width equal to the width of the picture. Atile scan is a specific sequential ordering of CTUs partitioning apicture in which the CTUs are ordered consecutively in CTU raster scanin a tile whereas tiles in a picture are ordered consecutively in araster scan of the tiles of the picture. A slice includes an integernumber of bricks of a picture that may be exclusively contained in asingle NAL unit. A slice may consist of either a number of completetiles or only a consecutive sequence of complete bricks of one tile.Tile groups and slices may be used interchangeably in the presentdisclosure. For example, in the present disclosure, a tile group/tilegroup header may be called a slice/slice header.

A pixel or a pel may mean a smallest unit constituting one picture (orimage). Also, ‘sample’ may be used as a term corresponding to a pixel. Asample may generally represent a pixel or a value of a pixel, and mayrepresent only a pixel/pixel value of a luma component or only apixel/pixel value of a chroma component.

A unit may represent a basic unit of image processing. The unit mayinclude at least one of a specific region of the picture and informationrelated to the region. One unit may include one luma block and twochroma (e.g., cb, cr) blocks. The unit may be used interchangeably withterms such as block or area in some cases. In a general case, an M×Nblock may include samples (or sample arrays) or a set (or array) oftransform coefficients of M columns and N rows.

In the present description, “A or B” may mean “only A”, “only B” or“both A and B”. In other words, in the present specification, “A or B”may be interpreted as “A and/or B”. For example, “A, B or C” hereinmeans “only A”, “only B”, “only C”, or “any and any combination of A, Band C”.

A slash (/) or a comma (comma) used in the present description may mean“and/or”. For example, “A/B” may mean “A and/or B”. Accordingly, “A/B”may mean “only A”, “only B”, or “both A and B”. For example, “A, B, C”may mean “A, B, or C”.

In the present description, “at least one of A and B” may mean “only A”,“only B”, or “both A and B”. In addition, in the present description,the expression “at least one of A or B” or “at least one of A and/or B”may be interpreted the same as “at least one of A and B”.

In addition, in the present description, “at least one of A, B and C”means “only A”, “only B”, “only C”, or “any combination of A, B and C”.Also, “at least one of A, B or C” or “at least one of A, B and/or C” maymean “at least one of A, B and C”.

In addition, parentheses used in the present description may mean “forexample”. Specifically, when “prediction (intra prediction)” isindicated, “intra prediction” may be proposed as an example of“prediction”. In other words, “prediction” in the present description isnot limited to “intra prediction”, and “intra prediction” may beproposed as an example of “prediction”. Also, even when “prediction(i.e., intra prediction)” is indicated, “intra prediction” may beproposed as an example of “prediction”.

In the present description, technical features that are individuallydescribed within one drawing may be implemented individually or may beimplemented at the same time.

The following drawings were created to explain a specific example of thepresent description. Since the names of specific devices described inthe drawings or the names of specific signals/messages/fields arepresented by way of example, the technical features of the presentdescription are not limited to the specific names used in the followingdrawings.

FIG. 2 is a schematic diagram illustrating a configuration of avideo/image encoding apparatus to which the embodiment(s) of the presentdisclosure may be applied. Hereinafter, the video encoding apparatus mayinclude an image encoding apparatus.

Referring to FIG. 2, the encoding apparatus 200 includes an imagepartitioner 210, a predictor 220, a residual processor 230, and anentropy encoder 240, an adder 250, a filter 260, and a memory 270. Thepredictor 220 may include an inter predictor 221 and an intra predictor222. The residual processor 230 may include a transformer 232, aquantizer 233, a dequantizer 234, and an inverse transformer 235. Theresidual processor 230 may further include a subtractor 231. The adder250 may be called a reconstructor or a reconstructed block generator.The image partitioner 210, the predictor 220, the residual processor230, the entropy encoder 240, the adder 250, and the filter 260 may beconfigured by at least one hardware component (e.g., an encoder chipsetor processor) according to an embodiment. In addition, the memory 270may include a decoded picture buffer (DPB) or may be configured by adigital storage medium. The hardware component may further include thememory 270 as an internal/external component.

The image partitioner 210 may partition an input image (or a picture ora frame) input to the encoding apparatus 200 into one or moreprocessors. For example, the processor may be called a coding unit (CU).In this case, the coding unit may be recursively partitioned accordingto a quad-tree binary-tree ternary-tree (QTBTTT) structure from a codingtree unit (CTU) or a largest coding unit (LCU). For example, one codingunit may be partitioned into a plurality of coding units of a deeperdepth based on a quad tree structure, a binary tree structure, and/or aternary structure. In this case, for example, the quad tree structuremay be applied first and the binary tree structure and/or ternarystructure may be applied later. Alternatively, the binary tree structuremay be applied first. The coding procedure according to the presentdisclosure may be performed based on the final coding unit that is nolonger partitioned. In this case, the largest coding unit may be used asthe final coding unit based on coding efficiency according to imagecharacteristics, or if necessary, the coding unit may be recursivelypartitioned into coding units of deeper depth and a coding unit havingan optimal size may be used as the final coding unit. Here, the codingprocedure may include a procedure of prediction, transform, andreconstruction, which will be described later. As another example, theprocessor may further include a prediction unit (PU) or a transform unit(TU). In this case, the prediction unit and the transform unit may besplit or partitioned from the aforementioned final coding unit. Theprediction unit may be a unit of sample prediction, and the transformunit may be a unit for deriving a transform coefficient and/or a unitfor deriving a residual signal from the transform coefficient.

The unit may be used interchangeably with terms such as block or area insome cases. In a general case, an M×N block may represent a set ofsamples or transform coefficients composed of M columns and N rows. Asample may generally represent a pixel or a value of a pixel, mayrepresent only a pixel/pixel value of a luma component or represent onlya pixel/pixel value of a chroma component. A sample may be used as aterm corresponding to one picture (or image) for a pixel or a pel.

In the encoding apparatus 200, a prediction signal (predicted block,prediction sample array) output from the inter predictor 221 or theintra predictor 222 is subtracted from an input image signal (originalblock, original sample array) to generate a residual signal residualblock, residual sample array), and the generated residual signal istransmitted to the transformer 232. In this case, as shown, a unit forsubtracting a prediction signal (predicted block, prediction samplearray) from the input image signal (original block, original samplearray) in the encoder 200 may be called a subtractor 231. The predictormay perform prediction on a block to be processed (hereinafter, referredto as a current block) and generate a predicted block includingprediction samples for the current block. The predictor may determinewhether intra prediction or inter prediction is applied on a currentblock or CU basis. As described later in the description of eachprediction mode, the predictor may generate various information relatedto prediction, such as prediction mode information, and transmit thegenerated information to the entropy encoder 240. The information on theprediction may be encoded in the entropy encoder 240 and output in theform of a bit stream.

The intra predictor 222 may predict the current block by referring tothe samples in the current picture. The referred samples may be locatedin the neighborhood of the current block or may be located apartaccording to the prediction mode. In the intra prediction, predictionmodes may include a plurality of non-directional modes and a pluralityof directional modes. The non-directional mode may include, for example,a DC mode and a planar mode. The directional mode may include, forexample, 33 directional prediction modes or 65 directional predictionmodes according to the degree of detail of the prediction direction.However, this is merely an example, more or less directional predictionmodes may be used depending on a setting. The intra predictor 222 maydetermine the prediction mode applied to the current block by using aprediction mode applied to a neighboring block.

The inter predictor 221 may derive a predicted block for the currentblock based on a reference block (reference sample array) specified by amotion vector on a reference picture. Here, in order to reduce theamount of motion information transmitted in the inter prediction mode,the motion information may be predicted in units of blocks, sub-blocks,or samples based on correlation of motion information between theneighboring block and the current block. The motion information mayinclude a motion vector and a reference picture index. The motioninformation may further include inter prediction direction (L0prediction, L1 prediction, Bi prediction, etc.) information. In the caseof inter prediction, the neighboring block may include a spatialneighboring block present in the current picture and a temporalneighboring block present in the reference picture. The referencepicture including the reference block and the reference pictureincluding the temporal neighboring block may be the same or different.The temporal neighboring block may be called a collocated referenceblock, a co-located CU (colCU), and the like, and the reference pictureincluding the temporal neighboring block may be called a collocatedpicture (colPic). For example, the inter predictor 221 may configure amotion information candidate list based on neighboring blocks andgenerate information indicating which candidate is used to derive amotion vector and/or a reference picture index of the current block.Inter prediction may be performed based on various prediction modes. Forexample, in the case of a skip mode and a merge mode, the interpredictor 221 may use motion information of the neighboring block asmotion information of the current block. In the skip mode, unlike themerge mode, the residual signal may not be transmitted. In the case ofthe motion vector prediction (MVP) mode, the motion vector of theneighboring block may be used as a motion vector predictor and themotion vector of the current block may be indicated by signaling amotion vector difference.

The predictor 220 may generate a prediction signal based on variousprediction methods described below. For example, the predictor may notonly apply intra prediction or inter prediction to predict one block butalso simultaneously apply both intra prediction and inter prediction.This may be called combined inter and intra prediction (CIIP). Inaddition, the predictor may be based on an intra block copy (IBC)prediction mode or a palette mode for prediction of a block. The IBCprediction mode or palette mode may be used for content image/videocoding of a game or the like, for example, screen content coding (SCC).The IBC basically performs prediction in the current picture but may beperformed similarly to inter prediction in that a reference block isderived in the current picture. That is, the IBC may use at least one ofthe inter prediction techniques described in the present disclosure. Thepalette mode may be considered as an example of intra coding or intraprediction. When the palette mode is applied, a sample value within apicture may be signaled based on information on the palette table andthe palette index.

The prediction signal generated by the predictor (including the interpredictor 221 and/or the intra predictor 222) may be used to generate areconstructed signal or to generate a residual signal. The transformer232 may generate transform coefficients by applying a transformtechnique to the residual signal. For example, the transform techniquemay include at least one of a discrete cosine transform (DCT), adiscrete sine transform (DST), a Karhunen-loeve transform (KLT), agraph-based transform (GBT), or a conditionally non-linear transform(CNT). Here, the GBT means transform obtained from a graph whenrelationship information between pixels is represented by the graph. TheCNT refers to transform generated based on a prediction signal generatedusing all previously reconstructed pixels. In addition, the transformprocess may be applied to square pixel blocks having the same size ormay be applied to blocks having a variable size rather than square.

The quantizer 233 may quantize the transform coefficients and transmitthem to the entropy encoder 240 and the entropy encoder 240 may encodethe quantized signal (information on the quantized transformcoefficients) and output a bit stream. The information on the quantizedtransform coefficients may be referred to as residual information. Thequantizer 233 may rearrange block type quantized transform coefficientsinto a one-dimensional vector form based on a coefficient scanning orderand generate information on the quantized transform coefficients basedon the quantized transform coefficients in the one-dimensional vectorform. Information on transform coefficients may be generated. Theentropy encoder 240 may perform various encoding methods such as, forexample, exponential Golomb, context-adaptive variable length coding(CAVLC), context-adaptive binary arithmetic coding (CABAC), and thelike. The entropy encoder 240 may encode information necessary forvideo/image reconstruction other than quantized transform coefficients(e.g., values of syntax elements, etc.) together or separately. Encodedinformation (e.g., encoded video/image information) may be transmittedor stored in units of NALs (network abstraction layer) in the form of abit stream. The video/image information may further include informationon various parameter sets such as an adaptation parameter set (APS), apicture parameter set (PPS), a sequence parameter set (SPS), or a videoparameter set (VPS). In addition, the video/image information mayfurther include general constraint information. In the presentdisclosure, information and/or syntax elements transmitted/signaled fromthe encoding apparatus to the decoding apparatus may be included invideo/picture information. The video/image information may be encodedthrough the above-described encoding procedure and included in the bitstream. The bit stream may be transmitted over a network or may bestored in a digital storage medium. The network may include abroadcasting network and/or a communication network, and the digitalstorage medium may include various storage media such as USB, SD, CD,DVD, Blu-ray, HDD, SSD, and the like. A transmitter (not shown)transmitting a signal output from the entropy encoder 240 and/or astorage unit (not shown) storing the signal may be included asinternal/external element of the encoding apparatus 200, andalternatively, the transmitter may be included in the entropy encoder240.

The quantized transform coefficients output from the quantizer 233 maybe used to generate a prediction signal. For example, the residualsignal (residual block or residual samples) may be reconstructed byapplying dequantization and inverse transform to the quantized transformcoefficients through the dequantizer 234 and the inverse transformer235. The adder 250 adds the reconstructed residual signal to theprediction signal output from the inter predictor 221 or the intrapredictor 222 to generate a reconstructed signal (reconstructed picture,reconstructed block, reconstructed sample array). If there is noresidual for the block to be processed, such as a case where the skipmode is applied, the predicted block may be used as the reconstructedblock. The adder 250 may be called a reconstructor or a reconstructedblock generator. The generated reconstructed signal may be used forintra prediction of a next block to be processed in the current pictureand may be used for inter prediction of a next picture through filteringas described below.

Meanwhile, luma mapping with chroma scaling (LMCS) may be applied duringpicture encoding and/or reconstruction.

The filter 260 may improve subjective/objective image quality byapplying filtering to the reconstructed signal. For example, the filter260 may generate a modified reconstructed picture by applying variousfiltering methods to the reconstructed picture and store the modifiedreconstructed picture in the memory 270, specifically, a DPB of thememory 270. The various filtering methods may include, for example,deblocking filtering, a sample adaptive offset, an adaptive loop filter,a bilateral filter, and the like. The filter 260 may generate variousinformation related to the filtering and transmit the generatedinformation to the entropy encoder 240 as described later in thedescription of each filtering method. The information related to thefiltering may be encoded by the entropy encoder 240 and output in theform of a bit stream.

The modified reconstructed picture transmitted to the memory 270 may beused as the reference picture in the inter predictor 221. When the interprediction is applied through the encoding apparatus, predictionmismatch between the encoding apparatus 200 and the decoding apparatus300 may be avoided and encoding efficiency may be improved.

The DPB of the memory 270 DPB may store the modified reconstructedpicture for use as a reference picture in the inter predictor 221. Thememory 270 may store the motion information of the block from which themotion information in the current picture is derived (or encoded) and/orthe motion information of the blocks in the picture that have alreadybeen reconstructed. The stored motion information may be transmitted tothe inter predictor 221 and used as the motion information of thespatial neighboring block or the motion information of the temporalneighboring block. The memory 270 may store reconstructed samples ofreconstructed blocks in the current picture and may transfer thereconstructed samples to the intra predictor 222.

FIG. 3 is a schematic diagram illustrating a configuration of avideo/image decoding apparatus to which the embodiment(s) of the presentdisclosure may be applied.

Referring to FIG. 3, the decoding apparatus 300 may include an entropydecoder 310, a residual processor 320, a predictor 330, an adder 340, afilter 350, and a memory 360. The predictor 330 may include an interpredictor 331 and an intra predictor 332. The residual processor 320 mayinclude a dequantizer 321 and an inverse transformer 322. The entropydecoder 310, the residual processor 320, the predictor 330, the adder340, and the filter 350 may be configured by a hardware component (e.g.,a decoder chipset or a processor) according to an embodiment. Inaddition, the memory 360 may include a decoded picture buffer (DPB) ormay be configured by a digital storage medium. The hardware componentmay further include the memory 360 as an internal/external component.

When a bit stream including video/image information is input, thedecoding apparatus 300 may reconstruct an image corresponding to aprocess in which the video/image information is processed in theencoding apparatus of FIG. 2. For example, the decoding apparatus 300may derive units/blocks based on block partition related informationobtained from the bit stream. The decoding apparatus 300 may performdecoding using a processor applied in the encoding apparatus. Thus, theprocessor of decoding may be a coding unit, for example, and the codingunit may be partitioned according to a quad tree structure, binary treestructure and/or ternary tree structure from the coding tree unit or thelargest coding unit. One or more transform units may be derived from thecoding unit. The reconstructed image signal decoded and output throughthe decoding apparatus 300 may be reproduced through a reproducingapparatus.

The decoding apparatus 300 may receive a signal output from the encodingapparatus of FIG. 2 in the form of a bit stream, and the received signalmay be decoded through the entropy decoder 310. For example, the entropydecoder 310 may parse the bit stream to derive information (e.g.,video/image information) necessary for image reconstruction (or picturereconstruction). The video/image information may further includeinformation on various parameter sets such as an adaptation parameterset (APS), a picture parameter set (PPS), a sequence parameter set(SPS), or a video parameter set (VPS). In addition, the video/imageinformation may further include general constraint information. Thedecoding apparatus may further decode picture based on the informationon the parameter set and/or the general constraint information.Signaled/received information and/or syntax elements described later inthe present disclosure may be decoded may decode the decoding procedureand obtained from the bit stream. For example, the entropy decoder 310decodes the information in the bit stream based on a coding method suchas exponential Golomb coding, CAVLC, or CABAC, and output syntaxelements required for image reconstruction and quantized values oftransform coefficients for residual. More specifically, the CABACentropy decoding method may receive a bin corresponding to each syntaxelement in the bit stream, determine a context model using a decodingtarget syntax element information, decoding information of a decodingtarget block or information of a symbol/bin decoded in a previous stage,and perform an arithmetic decoding on the bin by predicting aprobability of occurrence of a bin according to the determined contextmodel, and generate a symbol corresponding to the value of each syntaxelement. In this case, the CABAC entropy decoding method may update thecontext model by using the information of the decoded symbol/bin for acontext model of a next symbol/bin after determining the context model.The information related to the prediction among the information decodedby the entropy decoder 310 may be provided to the predictor (the interpredictor 332 and the intra predictor 331), and the residual value onwhich the entropy decoding was performed in the entropy decoder 310,that is, the quantized transform coefficients and related parameterinformation, may be input to the residual processor 320. The residualprocessor 320 may derive the residual signal (the residual block, theresidual samples, the residual sample array). In addition, informationon filtering among information decoded by the entropy decoder 310 may beprovided to the filter 350. Meanwhile, a receiver (not shown) forreceiving a signal output from the encoding apparatus may be furtherconfigured as an internal/external element of the decoding apparatus300, or the receiver may be a component of the entropy decoder 310.Meanwhile, the decoding apparatus according to the present disclosuremay be referred to as a video/image/picture decoding apparatus, and thedecoding apparatus may be classified into an information decoder(video/image/picture information decoder) and a sample decoder(video/image/picture sample decoder). The information decoder mayinclude the entropy decoder 310, and the sample decoder may include atleast one of the dequantizer 321, the inverse transformer 322, the adder340, the filter 350, the memory 360, the inter predictor 332, and theintra predictor 331.

The dequantizer 321 may dequantize the quantized transform coefficientsand output the transform coefficients. The dequantizer 321 may rearrangethe quantized transform coefficients in the form of a two-dimensionalblock form. In this case, the rearrangement may be performed based onthe coefficient scanning order performed in the encoding apparatus. Thedequantizer 321 may perform dequantization on the quantized transformcoefficients by using a quantization parameter (e.g., quantization stepsize information) and obtain transform coefficients.

The inverse transformer 322 inversely transforms the transformcoefficients to obtain a residual signal (residual block, residualsample array).

The predictor may perform prediction on the current block and generate apredicted block including prediction samples for the current block. Thepredictor may determine whether intra prediction or inter prediction isapplied to the current block based on the information on the predictionoutput from the entropy decoder 310 and may determine a specificintra/inter prediction mode.

The predictor 320 may generate a prediction signal based on variousprediction methods described below. For example, the predictor may notonly apply intra prediction or inter prediction to predict one block butalso simultaneously apply intra prediction and inter prediction. Thismay be called combined inter and intra prediction (CIIP). In addition,the predictor may be based on an intra block copy (IBC) prediction modeor a palette mode for prediction of a block. The IBC prediction mode orpalette mode may be used for content image/video coding of a game or thelike, for example, screen content coding (SCC). The IBC basicallyperforms prediction in the current picture but may be performedsimilarly to inter prediction in that a reference block is derived inthe current picture. That is, the IBC may use at least one of the interprediction techniques described in the present disclosure. The palettemode may be considered as an example of intra coding or intraprediction. When the palette mode is applied, a sample value within apicture may be signaled based on information on the palette table andthe palette index.

The intra predictor 331 may predict the current block by referring tothe samples in the current picture. The referred samples may be locatedin the neighborhood of the current block or may be located apartaccording to the prediction mode. In the intra prediction, predictionmodes may include a plurality of non-directional modes and a pluralityof directional modes. The intra predictor 331 may determine theprediction mode applied to the current block by using a prediction modeapplied to a neighboring block.

The inter predictor 332 may derive a predicted block for the currentblock based on a reference block (reference sample array) specified by amotion vector on a reference picture. In this case, in order to reducethe amount of motion information transmitted in the inter predictionmode, motion information may be predicted in units of blocks,sub-blocks, or samples based on correlation of motion informationbetween the neighboring block and the current block. The motioninformation may include a motion vector and a reference picture index.The motion information may further include inter prediction direction(L0 prediction, L1 prediction, Bi prediction, etc.) information. In thecase of inter prediction, the neighboring block may include a spatialneighboring block present in the current picture and a temporalneighboring block present in the reference picture. For example, theinter predictor 332 may configure a motion information candidate listbased on neighboring blocks and derive a motion vector of the currentblock and/or a reference picture index based on the received candidateselection information. Inter prediction may be performed based onvarious prediction modes, and the information on the prediction mayinclude information indicating a mode of inter prediction for thecurrent block.

The adder 340 may generate a reconstructed signal (reconstructedpicture, reconstructed block, reconstructed sample array) by adding theobtained residual signal to the prediction signal (predicted block,predicted sample array) output from the predictor (including the interpredictor 332 and/or the intra predictor 331). If there is no residualfor the block to be processed, such as when the skip mode is applied,the predicted block may be used as the reconstructed block.

The adder 340 may be called reconstructor or a reconstructed blockgenerator. The generated reconstructed signal may be used for intraprediction of a next block to be processed in the current picture, maybe output through filtering as described below, or may be used for interprediction of a next picture.

Meanwhile, luma mapping with chroma scaling (LMCS) may be applied in thepicture decoding process.

The filter 350 may improve subjective/objective image quality byapplying filtering to the reconstructed signal. For example, the filter350 may generate a modified reconstructed picture by applying variousfiltering methods to the reconstructed picture and store the modifiedreconstructed picture in the memory 360, specifically, a DPB of thememory 360. The various filtering methods may include, for example,deblocking filtering, a sample adaptive offset, an adaptive loop filter,a bilateral filter, and the like.

The (modified) reconstructed picture stored in the DPB of the memory 360may be used as a reference picture in the inter predictor 332. Thememory 360 may store the motion information of the block from which themotion information in the current picture is derived (or decoded) and/orthe motion information of the blocks in the picture that have alreadybeen reconstructed. The stored motion information may be transmitted tothe inter predictor 260 so as to be utilized as the motion informationof the spatial neighboring block or the motion information of thetemporal neighboring block. The memory 360 may store reconstructedsamples of reconstructed blocks in the current picture and transfer thereconstructed samples to the intra predictor 331.

In the present disclosure, the embodiments described in the filter 260,the inter predictor 221, and the intra predictor 222 of the encodingapparatus 200 may be the same as or respectively applied to correspondto the filter 350, the inter predictor 332, and the intra predictor 331of the decoding apparatus 300. The same may also apply to the unit 332and the intra predictor 331.

In the present disclosure, at least one of quantization/inversequantization and/or transform/inverse transform may be omitted. When thequantization/inverse quantization is omitted, the quantized transformcoefficients may be called transform coefficients. When thetransform/inverse transform is omitted, the transform coefficients maybe called coefficients or residual coefficients, or may still be calledtransform coefficients for uniformity of expression.

In the present disclosure, a quantized transform coefficient and atransform coefficient may be referred to as a transform coefficient anda scaled transform coefficient, respectively. In this case, the residualinformation may include information on transform coefficient(s), and theinformation on the transform coefficient(s) may be signaled throughresidual coding syntax. Transform coefficients may be derived based onthe residual information (or the information on the transformcoefficient(s)), and scaled transform coefficients may be derived byinverse transforming (scaling) on the transform coefficients. Residualsamples may be derived based on the inverse transforming (transforming)on the scaled transform coefficients. This may be applied/expressed inother parts of the present disclosure as well.

As described above, in performing video coding, prediction is performedto improve compression efficiency. Through this, a predicted blockincluding prediction samples for a current block as a block to be coded(i.e., a coding target block) may be generated. Here, the predictedblock includes prediction samples in a spatial domain (or pixel domain).The predicted block is derived in the same manner in an encodingapparatus and a decoding apparatus, and the encoding apparatus maysignal information (residual information) on residual between theoriginal block and the predicted block, rather than an original samplevalue of an original block, to the decoding apparatus, therebyincreasing image coding efficiency. The decoding apparatus may derive aresidual block including residual samples based on the residualinformation, add the residual block and the predicted block to generatereconstructed blocks including reconstructed samples, and generate areconstructed picture including the reconstructed blocks.

The residual information may be generated through a transform andquantization procedure. For example, the encoding apparatus may derive aresidual block between the original block and the predicted block,perform a transform procedure on residual samples (residual samplearray) included in the residual block to derive transform coefficients,perform a quantization procedure on the transform coefficients to derivequantized transform coefficients, and signal related residualinformation to the decoding apparatus (through a bit stream). Here, theresidual information may include value information of the quantizedtransform coefficients, location information, a transform technique, atransform kernel, a quantization parameter, and the like. The decodingapparatus may perform dequantization/inverse transform procedure basedon the residual information and derive residual samples (or residualblocks). The decoding apparatus may generate a reconstructed picturebased on the predicted block and the residual block. Also, for referencefor inter prediction of a picture afterward, the encoding apparatus mayalso dequantize/inverse-transform the quantized transform coefficientsto derive a residual block and generate a reconstructed picture basedthereon.

Intra prediction may refer to prediction that generates predictionsamples for a current block based on reference samples in a picture towhich the current block belongs (hereinafter, referred to as a currentpicture). When the intra prediction is applied to the current block,neighboring reference samples to be used for the intra prediction of thecurrent block may be derived. The neighboring reference samples of thecurrent block may include a sample adjacent to the left boundary of thecurrent block of size nW×nH and a total of 2×nH samples adjacent to thebottom-left of the current block, a sample adjacent to the top boundaryof the current block and a total of 2×nW samples adjacent to thetop-right and a sample adjacent to the top-left of the current block.Alternatively, the neighboring reference samples of the current blockmay include a plurality of columns of top neighboring samples and aplurality of rows of left neighboring samples. In addition, theneighboring reference samples of the current block may include a totalof nH samples adjacent to the right boundary of the current block ofsize nW×nH, a total of nW samples adjacent to the bottom boundary of thecurrent block and a sample adjacent to the bottom-right of the currentblock.

However, some of the neighboring reference samples of the current blockhave not yet been decoded or may not be available. In this case, thedecoder may construct neighboring reference samples to be used forprediction by substituting unavailable samples with available samples.Alternatively, neighboring reference samples to be used for predictionmay be configured through interpolation of available samples.

When the neighboring reference samples are derived, (i) a predictionsample may be derived based on the average or interpolation ofneighboring reference samples of the current block, or (ii) theprediction sample may be derived based on a reference sample existing ina specific (prediction) direction with respect to a prediction sampleamong the neighboring reference samples of the current block. The caseof (i) may be called a non-directional mode or a non-angular mode, andthe case of (ii) may be called a directional mode or an angular mode.

In addition, the prediction sample may be generated throughinterpolation of a first neighboring sample located in the predictiondirection of the intra prediction mode of the current block based on theprediction sample of the current block and a second neighboring samplelocated in a direction opposite to the prediction direction among theneighboring reference samples. The above-described case may be referredto as linear interpolation intra prediction (LIP). In addition, chromaprediction samples may be generated based on the luma samples using alinear model (LM). This case may be called an LM mode or a chromacomponent LM (CCLM) mode.

In addition, a temporary prediction sample of the current block isderived based on the filtered neighboring reference samples, and aprediction sample of the current block may also be derived by weightedsumming the temporary prediction sample and at least one referencesample derived according to the intra prediction mode among the existingneighboring reference samples, that is, unfiltered neighboring referencesamples. The above-described case may be referred to as positiondependent intra prediction (PDPC).

In addition, a reference sample line with the highest predictionaccuracy among neighboring multiple reference sample lines of thecurrent block is selected, and a prediction sample is derived using areference sample located in the prediction direction in the selectedline. In this case, intra prediction encoding may be performed byindicating (signaling) the used reference sample line to the decodingapparatus. The above-described case may be referred to asmulti-reference line intra prediction or MRL-based intra prediction.

In addition, the current block is divided into vertical or horizontalsub-partitions and intra prediction is performed based on the same intraprediction mode, but neighboring reference samples may be derived andused in units of the sub-partitions. That is, in this case, the intraprediction mode for the current block is equally applied to thesub-partitions, but the intra prediction performance may be improved insome cases by deriving and using the neighboring reference samples inunits of the sub-partitions. This prediction method may be calledintra-prediction based on intra sub-partitions (ISP).

The above-described intra prediction methods may be called intraprediction types to be distinguished from the intra prediction mode. Theintra prediction types may be referred to by various terms such as intraprediction technique or additional intra prediction modes. For example,the intra prediction types (or additional intra prediction modes, etc.)may include at least one of the aforementioned LIP, PDPC, MRL, and ISP.A general intra prediction method excluding a specific intra predictiontype such as LIP, PDPC, MRL, and ISP may be referred to as a normalintra prediction type. The normal intra prediction type may be generallyapplied when the above specific intra prediction type is not applied,and prediction may be performed based on the above-described intraprediction mode. Meanwhile, if necessary, post-processing filtering maybe performed on the derived prediction sample.

Specifically, the intra prediction process may include an intraprediction mode/type determination step, neighboring reference samplesderivation step, and an intra prediction mode/type based predictionsample derivation step. In addition, if necessary, a post-filtering stepmay be performed on the derived prediction sample.

When intra prediction is applied, an intra prediction mode applied tothe current block may be determined using an intra prediction mode of aneighboring block. For example, the decoding device may select one ofmost probable mode (MPM) candidates in the MPM list derived based onadditional candidate modes and an intra prediction mode of theneighboring block (e.g., the left and/or top neighboring block) of thecurrent block, or select one of the remaining intra prediction modes notincluded in the MPM candidates (and planar mode) based on the remainingintra prediction mode information. The MPM list may be configured toinclude or not include the planner mode as a candidate. For example,when the MPM list includes a planner mode as a candidate, the MPM listmay have 6 candidates, and when the MPM list does not include a plannermode as a candidate, the MPM list may have 5 candidates. When the MPMlist does not include the planar mode as a candidate, a not planar flag(e.g., intra_luma_not_planar_flag) representing whether the intraprediction mode of the current block is not the planar mode may besignaled. For example, the MPM flag may be signaled first, and the MPMindex and not planner flag may be signaled when the value of the MPMflag is 1. Also, the MPM index may be signaled when the value of the notplanner flag is 1. Here, the fact that the MPM list is configured not toinclude the planner mode as a candidate is that the planner mode isalways considered as MPM rather than that the planner mode is not MPM,thus, the flag (not planar flag) is signaled first to check whether itis the planar mode.

For example, whether the intra prediction mode applied to the currentblock is among the MPM candidates (and the planar mode) or the remainingmodes may be indicated based on the MPM flag (e.g.,intra_luma_mpm_flag). The MPM flag with a value of 1 may indicate thatthe intra prediction mode for the current block is within MPM candidates(and planar mode), and The MPM flag with a value of 0 may indicate thatthe intra prediction mode for the current block is not within MPMcandidates (and planar mode). The not planar flag (e.g.,intra_luma_not_planar_flag) with a value of 0 may indicate that theintra prediction mode for the current block is a planar mode, and thenot planar flag with a value of 1 may indicate that the intra predictionmode for the current block is not the planar mode. The MPM index may besignaled in the form of an mpm_idx or intra_luma_mpm_idx syntax element,and the remaining intra prediction mode information may be signaled inthe form of a rem_intra_luma_pred_mode or intra_luma_mpm_remaindersyntax element. For example, the remaining intra prediction modeinformation may indicate one of the remaining intra prediction modes notincluded in the MPM candidates (and planar mode) among all intraprediction modes by indexing in the order of prediction mode number. Theintra prediction mode may be an intra prediction mode for a lumacomponent (sample). Hereinafter, the intra prediction mode informationmay include at least one of the MPM flag (e.g., intra_luma_mpm_flag),the not planar flag (e.g., intra_luma_not_planar_flag), the MPM index(e.g., mpm_idx or intra_luma_mpm_idx), or the remaining intra predictionmode information (rem_intra_luma_luma_mpm_mode or intra_luma_mpminder).In the present disclosure, the MPM list may be referred to by variousterms such as an MPM candidate list and candModeList. When the MIP isapplied to the current block, a separate MPM flag (e.g.,intra_mip_mpm_flag) for the MIP, an MPM index (e.g., intra_mip_mpm_idx),and remaining intra prediction mode information (e.g.,intra_mip_mpm_remainder) may be signaled, and the not planar flag maynot be signaled.

In other words, in general, when a block partition for an image isperformed, the current block to be coded and a neighboring block havesimilar image characteristics. Therefore, there is a high probabilitythat the current block and the neighboring block have the same orsimilar intra prediction mode. Accordingly, the encoder may use theintra prediction mode of the neighboring block to encode the intraprediction mode of the current block.

For example, The decoding device/encoding device may construct a mostprobable modes (MPM) list for the current block. The MPM list may bereferred to as the MPM candidate list. Here, the MPM may refer to modesused to improve coding efficiency in consideration of the similaritybetween the current block and the neighboring blocks during intraprediction mode coding. As described above, the MPM list may beconstructed to include the planar mode, or may be constructed to excludethe planar mode. For example, when the MPM list includes the planarmode, the number of candidates in the MPM list may be 6. And, when theMPM list does not include the planar mode, the number of candidates inthe MPM list may be 5.

The encoder/decoder may construct an MPM list including five or sixMPMs.

In order to construct the MPM list, three types of modes, such asdefault intra modes, neighbor intra modes, and derived intra modes, maybe considered.

For the neighbor intra modes, two neighbor blocks, that is, a leftneighbor block and a top neighbor block, may be considered.

As described above, if the MPM list is constructed to not include aplanar mode, the planar mode may be excluded from the list, and thenumber of MPM list candidates may be set to five.

Furthermore, a non-directional mode (or a non-angle mode) among theintra prediction modes may include a DC mode based on an average ofneighbor reference samples of a current block or an interpolation-basedplanar mode.

Meanwhile, when inter prediction is applied, the predictor of theencoding apparatus/decoding apparatus may derive prediction samples byperforming inter prediction in units of blocks. The inter prediction maybe applied when performing the prediction on the current block. That is,the predictor (more specifically, inter predictor) of theencoding/decoding apparatus may derive prediction samples by performingthe inter prediction in units of the block. The inter prediction mayrepresent prediction derived by a method dependent to the data elements(e.g., sample values or motion information) of a picture(s) other thanthe current picture. When the inter prediction is applied to the currentblock, a predicted block (prediction sample array) for the current blockmay be derived based on a reference block (reference sample array)specified by the motion vector on the reference picture indicated by thereference picture index. In this case, in order to reduce an amount ofmotion information transmitted in the inter-prediction mode, the motioninformation of the current block may be predicted in units of a block, asubblock, or a sample based on a correlation of the motion informationbetween the neighboring block and the current block. The motioninformation may include the motion vector and the reference pictureindex. The motion information may further include inter-prediction type(L0 prediction, L1 prediction, Bi prediction, etc.) information. In thecase of applying the inter prediction, the neighboring block may includea spatial neighboring block which is present in the current picture anda temporal neighboring block which is present in the reference picture.A reference picture including the reference block and a referencepicture including the temporal neighboring block may be the same as eachother or different from each other. The temporal neighboring block maybe referred to as a name such as a collocated reference block, acollocated CU (colCU), etc., and the reference picture including thetemporal neighboring block may be referred to as a collocated picture(colPic). For example, a motion information candidate list may beconfigured based on the neighboring blocks of the current block and aflag or index information indicating which candidate is selected (used)may be signaled in order to derive the motion vector and/or referencepicture index of the current block. The inter prediction may beperformed based on various prediction modes and for example, in the caseof a skip mode and a merge mode, the motion information of the currentblock may be the same as the motion information of the selectedneighboring block. In the case of the skip mode, the residual signal maynot be transmitted unlike the merge mode. In the case of a motion vectorprediction (MVP) mode, the motion vector of the selected neighboringblock may be used as a motion vector predictor and a motion vectordifference may be signaled. In this case, the motion vector of thecurrent block may be derived by using a sum of the motion vectorpredictor and the motion vector difference.

The motion information may further include L0 motion information and/orL1 motion information according to the inter-prediction type (L0prediction, L1 prediction, Bi prediction, etc.). A L0-direction motionvector may be referred to as an L0 motion vector or MVL0 and anL1-direction motion vector may be referred to as an L1 motion vector orMVL1. A prediction based on the L0 motion vector may be referred to asan L0 prediction, a prediction based on the L1 motion vector may bereferred to as an L1 prediction, and a prediction based on both the L0motion vector and the L1 motion vector may be referred to as abi-prediction. Here, the L0 motion vector may indicate a motion vectorassociated with a reference picture list L0 and the L1 motion vector mayindicate a motion vector associated with a reference picture list L1.The reference picture list L0 may include pictures prior to the currentpicture in an output order and the reference picture list L1 may includepictures subsequent to the current picture in the output order, as thereference pictures. The prior pictures may be referred to as a forward(reference) picture and the subsequent pictures may be referred to as areverse (reference) picture. The reference picture list L0 may furtherinclude the pictures subsequent to the current picture in the outputorder as the reference pictures. In this case, the prior pictures may befirst indexed in the reference picture list L0 and the subsequentpictures may then be indexed. The reference picture list L1 may furtherinclude the pictures prior to the current picture in the output order asthe reference pictures. In this case, the subsequent pictures may befirst indexed in the reference picture list L1 and the prior picturesmay then be indexed. Here, the output order may correspond to a pictureorder count (POC) order.

A video/image encoding process based on inter prediction mayschematically include, for example, the following.

FIG. 4 illustrates an example of an inter prediction-based video/imageencoding method.

The encoding apparatus performs the inter prediction for the currentblock (S400). The encoding apparatus may derive the inter predictionmode and the motion information of the current block and generate theprediction samples of the current block. Here, an inter prediction modedetermining process, a motion information deriving process, and ageneration process of the prediction samples may be simultaneouslyperformed and any one process may be performed earlier than otherprocess. For example, the inter-prediction unit of the encodingapparatus may include a prediction mode determination unit, a motioninformation derivation unit, and a prediction sample derivation unit,and the prediction mode determination unit may determine the predictionmode for the current block, the motion information derivation unit mayderive the motion information of the current block, and the predictionsample derivation unit may derive the prediction samples of the currentblock. For example, the inter-prediction unit of the encoding apparatusmay search a block similar to the current block in a predetermined area(search area) of reference pictures through motion estimation and derivea reference block in which a difference from the current block isminimum or is equal to or less than a predetermined criterion. Areference picture index indicating a reference picture at which thereference block is positioned may be derived based thereon and a motionvector may be derived based on a difference in location between thereference block and the current block. The encoding apparatus maydetermine a mode applied to the current block among various predictionmodes. The encoding apparatus may compare RD cost for the variousprediction modes and determine an optimal prediction mode for thecurrent block.

For example, when the skip mode or the merge mode is applied to thecurrent block, the encoding apparatus may configure a merging candidatelist to be described below and derive a reference block in which adifference from the current block is minimum or is equal to or less thana predetermined criterion among reference blocks indicated by mergecandidates included in the merging candidate list. In this case, a mergecandidate associated with the derived reference block may be selectedand merge index information indicating the selected merge candidate maybe generated and signaled to the decoding apparatus. The motioninformation of the current block may be derived by using the motioninformation of the selected merge candidate.

As another example, when an (A)MVP mode is applied to the current block,the encoding apparatus may configure an (A)MVP candidate list to bedescribed below and use a motion vector of a selected mvp candidateamong motion vector predictor (mvp) candidates included in the (A)MVPcandidate list as the mvp of the current block. In this case, forexample, the motion vector indicating the reference block derived by themotion estimation may be used as the motion vector of the current blockand an mvp candidate having a motion vector with a smallest differencefrom the motion vector of the current block among the mvp candidates maybecome the selected mvp candidate. A motion vector difference (MVD)which is a difference obtained by subtracting the mvp from the motionvector of the current block may be derived. In this case, theinformation on the MVD may be signaled to the decoding apparatus.Further, when the (A)MVP mode is applied, the value of the referencepicture index may be configured as reference picture index informationand separately signaled to the decoding apparatus.

The encoding apparatus may derive the residual samples based on thepredicted samples (S410). The encoding apparatus may derive the residualsamples by comparing original samples and the prediction samples of thecurrent block.

The encoding apparatus encodes image information including predictioninformation and residual information (S420). The encoding apparatus mayoutput the encoded image information in the form of a bit stream. Theprediction information may include information on prediction modeinformation (e.g., skip flag, merge flag or mode index, etc.) andinformation on motion information as information related to theprediction procedure. The information on the motion information mayinclude candidate selection information (e.g., merge index, mvp flag ormvp index) which is information for deriving the motion vector. Further,the information on the motion information may include the information onthe MVD and/or the reference picture index information. Further, theinformation on the motion information may include information indicatingwhether to apply the L0 prediction, the L1 prediction, or thebi-prediction. The residual information is information on the residualsamples. The residual information may include information on quantizedtransform coefficients for the residual samples.

An output bit stream may be stored in a (digital) storage medium andtransferred to the decoding apparatus or transferred to the decodingapparatus via the network.

Meanwhile, as described above, the encoding apparatus may generate areconstructed picture (including reconstructed samples and reconstructedblocks) based on the reference samples and the residual samples. This isto derive the same prediction result as that performed by the decodingapparatus, and as a result, coding efficiency may be increased.Accordingly, the encoding apparatus may store the reconstruction picture(or reconstruction samples or reconstruction blocks) in the memory andutilize the reconstruction picture as the reference picture. The in-loopfiltering process may be further applied to the reconstruction pictureas described above.

A video/image decoding process based on inter prediction mayschematically include, for example, the following.

FIG. 5 illustrates an example of an inter prediction-based video/imagedecoding method.

Referring to FIG. 5, the decoding apparatus may perform an operationcorresponding to the operation performed by the encoding apparatus. Thedecoding apparatus may perform the prediction for the current blockbased on received prediction information and derive the predictionsamples.

Specifically, the decoding apparatus may determine the prediction modefor the current block based on the received prediction information(S500). The decoding apparatus may determine which inter prediction modeis applied to the current block based on the prediction mode informationin the prediction information.

For example, it may be determined whether the merge mode or the (A)MVPmode is applied to the current block based on the merge flag.Alternatively, one of various inter prediction mode candidates may beselected based on the mode index. The inter prediction mode candidatesmay include a skip mode, a merge mode, and/or an (A)MVP mode or mayinclude various inter prediction modes to be described below.

The decoding apparatus derives the motion information of the currentblock based on the determined inter prediction mode (S510). For example,when the skip mode or the merge mode is applied to the current block,the decoding apparatus may configure the merge candidate list to bedescribed below and select one merge candidate among the mergecandidates included in the merge candidate list. Here, the selection maybe performed based on the selection information (merge index). Themotion information of the current block may be derived by using themotion information of the selected merge candidate. The motioninformation of the selected merge candidate may be used as the motioninformation of the current block.

As another example, when an (A)MVP mode is applied to the current block,the decoding apparatus may configure an (A)MVP candidate list to bedescribed below and use a motion vector of a selected mvp candidateamong motion vector predictor (mvp) candidates included in the (A)MVPcandidate list as the mvp of the current block. Here, the selection maybe performed based on the selection information (mvp flag or mvp index).In this case, the MVD of the current block may be derived based on theinformation on the MVD, and the motion vector of the current block maybe derived based on the mvp of the current block and the MVD. Further,the reference picture index of the current block may be derived based onthe reference picture index information. The picture indicated by thereference picture index in the reference picture list for the currentblock may be derived as the reference picture referred for the interprediction of the current block.

Meanwhile, as described below, the motion information of the currentblock may be derived without a candidate list configuration and in thiscase, the motion information of the current block may be derivedaccording to a procedure disclosed in the prediction mode. In this case,the candidate list configuration may be omitted.

The decoding apparatus may generate the prediction samples for thecurrent block based on the motion information of the current block(S520). In this case, the reference picture may be derived based on thereference picture index of the current block and the prediction samplesof the current block may be derived by using the samples of thereference block indicated by the motion vector of the current block onthe reference picture. In this case, in some cases, a predicted samplefiltering procedure for all or some of the prediction samples of thecurrent block may be further performed.

For example, the inter-prediction unit of the decoding apparatus mayinclude a prediction mode determination unit, a motion informationderivation unit, and a prediction sample derivation unit, and theprediction mode determination unit may determine the prediction mode forthe current block based on the received prediction mode information, themotion information derivation unit may derive the motion information(the motion vector and/or reference picture index) of the current blockbased on the information on the received motion information, and theprediction sample derivation unit may derive the predicted samples ofthe current block.

The decoding apparatus generates the residual samples for the currentblock based on the received residual information (S530). The decodingapparatus may generate the reconstruction samples for the current blockbased on the prediction samples and the residual samples and generatethe reconstruction picture based on the generated reconstruction samples(S540). Thereafter, the in-loop filtering procedure may be furtherapplied to the reconstruction picture as described above.

FIG. 6 schematically shows an inter prediction procedure.

Referring to FIG. 6, as described above, the inter prediction processmay include an inter prediction mode determination step, a motioninformation derivation step according to the determined prediction mode,and a prediction processing (prediction sample generation) step based onthe derived motion information. The inter prediction process may beperformed by the encoding apparatus and the decoding apparatus asdescribed above. In this document, a coding device may include theencoding apparatus and/or the decoding apparatus.

Referring to FIG. 6, the coding apparatus determines an inter predictionmode for the current block (S600). Various inter prediction modes may beused for the prediction of the current block in the picture. Forexample, various modes, such as a merge mode, a skip mode, a motionvector prediction (MVP) mode, an affine mode, a subblock merge mode, amerge with MVD (MMVD) mode, and a historical motion vector prediction(HMVP) mode may be used. A decoder side motion vector refinement (DMVR)mode, an adaptive motion vector resolution (AMVR) mode, a bi-predictionwith CU-level weight (BCW), a bi-directional optical flow (BDOF), andthe like may be further used as additional modes. The affine mode mayalso be referred to as an affine motion prediction mode. The MVP modemay also be referred to as an advanced motion vector prediction (AMVP)mode. In the present document, some modes and/or motion informationcandidates derived by some modes may also be included in one of motioninformation-related candidates in other modes. For example, the HMVPcandidate may be added to the merge candidate of the merge/skip modes,or also be added to an mvp candidate of the MVP mode. If the HMVPcandidate is used as the motion information candidate of the merge modeor the skip mode, the HMVP candidate may be referred to as the HMVPmerge candidate.

The prediction mode information indicating the inter prediction mode ofthe current block may be signaled from the encoding apparatus to thedecoding apparatus. In this case, the prediction mode information may beincluded in the bit stream and received by the decoding apparatus. Theprediction mode information may include index information indicating oneof multiple candidate modes. Alternatively, the inter prediction modemay be indicated through a hierarchical signaling of flag information.In this case, the prediction mode information may include one or moreflags. For example, whether to apply the skip mode may be indicated bysignaling a skip flag, whether to apply the merge mode may be indicatedby signaling a merge flag when the skip mode is not applied, and it isindicated that the MVP mode is applied or a flag for additionaldistinguishing may be further signaled when the merge mode is notapplied. The affine mode may be signaled as an independent mode orsignaled as a dependent mode on the merge mode or the MVP mode. Forexample, the affine mode may include an affine merge mode and an affineMVP mode.

The coding apparatus derives motion information for the current block(S610). Motion information derivation may be derived based on the interprediction mode.

The coding apparatus may perform inter prediction using motioninformation of the current block. The encoding apparatus may deriveoptimal motion information for the current block through a motionestimation procedure. For example, the encoding apparatus may search asimilar reference block having a high correlation in units of afractional pixel within a predetermined search range in the referencepicture by using an original block in an original picture for thecurrent block and derive the motion information through the searchedreference block. The similarity of the block may be derived based on adifference of phase based sample values. For example, the similarity ofthe block may be calculated based on a sum of absolute differences (SAD)between the current block (or a template of the current block) and thereference block (or the template of the reference block). In this case,the motion information may be derived based on a reference block havinga smallest SAD in a search area. The derived motion information may besignaled to the decoding apparatus according to various methods based onthe inter prediction mode.

The coding apparatus performs inter prediction based on motioninformation for the current block (S620). The coding apparatus mayderive prediction sample(s) for the current block based on the motioninformation. A current block including prediction samples may bereferred to as a predicted block.

Meanwhile, as described above, the encoding apparatus may performvarious encoding methods such as exponential Golomb, context-adaptivevariable length coding (CAVLC), and context-adaptive binary arithmeticcoding (CABAC). In addition, the decoding apparatus may decodeinformation in a bitstream based on a coding method such as exponentialGolomb coding, CAVLC or CABAC, and output a value of a syntax elementrequired for image reconstruction and quantized values of transformcoefficients related to residuals.

For example, the coding methods described above may be performed asdescribed below.

FIG. 7 exemplarily shows context-adaptive binary arithmetic coding(CABAC) for encoding a syntax element. For example, in the CABACencoding process, when an input signal is a syntax element, rather thana binary value, the encoding apparatus may convert the input signal intoa binary value by binarizing the value of the input signal. In addition,when the input signal is already a binary value (i.e., when the value ofthe input signal is a binary value), binarization may not be performedand may be bypassed. Here, each binary number 0 or 1 constituting abinary value may be referred to as a bin. For example, if a binarystring after binarization is 110, each of 1, 1, and 0 is called one bin.The bin(s) for one syntax element may indicate a value of the syntaxelement.

Thereafter, the binarized bins of the syntax element may be input to aregular coding engine or a bypass coding engine. The regular codingengine of the encoding apparatus may allocate a context model reflectinga probability value to the corresponding bin, and may encode thecorresponding bin based on the allocated context model. The regularcoding engine of the encoding apparatus may update a context model foreach bin after performing encoding on each bin. A bin encoded asdescribed above may be referred to as a context-coded bin.

Meanwhile, when the binarized bins of the syntax element are input tothe bypass coding engine, they may be coded as follows. For example, thebypass coding engine of the encoding apparatus omits a procedure ofestimating a probability with respect to an input bin and a procedure ofupdating a probability model applied to the bin after encoding. Whenbypass encoding is applied, the encoding apparatus may encode the inputbin by applying a uniform probability distribution instead of allocatinga context model, thereby improving an encoding rate. The bin encoded asdescribed above may be referred to as a bypass bin.

Entropy decoding may represent a process of performing the same processas the entropy encoding described above in reverse order.

For example, when a syntax element is decoded based on a context model,the decoding apparatus may receive a bin corresponding to the syntaxelement through a bitstream, determine a context model using the syntaxelement and decoding information of a decoding target block or aneighbor block or information of a symbol/bin decoded in a previousstage, predict an occurrence probability of the received bin accordingto the determined context model, and perform an arithmetic decoding onthe bin to derive a value of the syntax element. Thereafter, a contextmodel of a bin which is decoded next may be updated with the determinedcontext model.

Also, for example, when a syntax element is bypass-decoded, the decodingapparatus may receive a bin corresponding to the syntax element througha bitstream, and decode the input bin by applying a uniform probabilitydistribution. In this case, the procedure of the decoding apparatus forderiving the context model of the syntax element and the procedure ofupdating the context model applied to the bin after decoding may beomitted.

As described above, residual samples may be derived as quantizedtransform coefficients through transform and quantization processes. Thequantized transform coefficients may also be referred to as transformcoefficients. In this case, the transform coefficients in a block may besignaled in the form of residual information. The residual informationmay include a residual coding syntax. That is, the encoding apparatusmay configure a residual coding syntax with residual information, encodethe same, and output it in the form of a bitstream, and the decodingapparatus may decode the residual coding syntax from the bitstream andderive residual (quantized) transform coefficients. The residual codingsyntax may include syntax elements representing whether transform wasapplied to the corresponding block, a location of a last effectivetransform coefficient in the block, whether an effective transformcoefficient exists in the subblock, a size/sign of the effectivetransform coefficient, and the like, as will be described later.

For example, the (quantized) transformation coefficients (i.e., theresidual information) may be encoded and/or decoded based on syntaxelements such as transform_skip_flag, last_sig_coeff_x_prefix,last_sig_coeff_y_prefix, last_sig_coeff_x_suffix,last_sig_coeff_y_suffix, coded_sub_block_flag, sig_coeff_flag,par_level_flag, abs_level_gt1_flag, abs_level_gt3_flag, abs_remainder,coeff_sign_flag, dec_abs_level, mts_jdx. Syntax elements related toresidual data encoding/decoding may be represented as shown in thefollowing table.

TABLE 1 residual coding( x0, y0, log2TbWidth, log2TbHeight, cIdx ) {Descriptor  if( transform_skip_enabled_flag && ( cIdx ! = 0 ||tu_mts_flag[ x0 ][ y0 ] = = 0) &&   ( log2TbWidth <= 2) && (log2TbHeight <= 2 ) )   transform_skip_flag[ x0 ][ y0 ][ cIdx ] ae(v) last_sig_coeff_x_prefix ae(v)  last_sig_coeff_y_prefix ae(v)  if(last_sig_coeff_x_prefix > 3)   last_sig_coeff_x_suffix ae(v)  if(last_sig_coeff_y_prefix > 3)   last_sig_coeff_y_suffix ae(v)  log2SbSize= ( Min( log2TbWidth, log2TbHeight) < 2 ? 1 : 2)  numSbCoeff = 1 << (log2SbSize << 1)  lastScanPos = numSbCoeff  lastSubBlock = ( 1 << (log2TbWidth + log2TbHeight − 2 * log2SbSize ) ) − 1  do {   if(lastScanPos = = 0) {    lastScanPos − numSbCoeff    lastSubBlock− −   }  lastScanPos− −   xS − DiagScanOrder[ log2TbWidth − log2SbSize ][log2TbHeight − log2SbSize ]         [ lastSubBlock ][ 0 ]   yS −DiagScanOrder[ log2TbWidth − log2SbSize ][ log2TbHeight − log2SbSize ]        [ lastSubBlock ][ 1 ]   xC − ( xS << log2SbSize ) +        DiagScanOrder[ log2SbSize ][ log2SbSize ][ lastScanPos ][ 0 ]  yC − ( yS << log2SbSize ) +         DiagScanOrder[ log2SbSize ][log2SbSize ][ lastScanPos ][ 1 ]  } while( ( xC != LastSignificantCoeffX) || ( yC != LastSignificantCoeffY ) )  numSigCoeff = 0  QState − 0 for( i = lastSubBlock; i >= 0; i− −) {   startQStateSb = QState   xS −DiagScanOrder[ log2TbWidth − log2SbSize ][ log2TbHeight − log2SbSize ]        [ lastSubBlock ][ 0 ]   yS = DiagScanOrder[ log2TbWidth −log2SbSize ][ log2TbHeight − log2SbSize ]         [ lastSubBlock ][ 1 ]  inferSbDcSigCoeffFlag = 0   if( (i < lastSubBlock ) && ( i > 0 ) ) {   coded_sub_block tlag[ xS ][ yS ] ae(v)    inferSbDcSigCoeffFlag = 1  }   firstSigScanPosSb = numSbCoeff   lastSigScanPosSb = −1  remBinsPass1 = ( log2SbSize < 2 ? 6 : 28)   remBinsPass2 = (log2SbSize < 2 ? 2 : 4)   firstPosMode0 = ( i = = lastSubBlock ?lastScanPos − 1 : numSbCoeff − 1)   firstPosMode1 = −1   firstPosMode2 =−1   for( n = (i = = firstPosMode0; n >= 0 && remBinsPass1 >= 3; n − −){    xC = ( xS << log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize][ n ][ 0 ]    yC = ( yS << log2SbSize ) + DiagScanOrder[ log2SbSize ][log2SbSize ][ n ][ 1 ]    if( coded sub block flag[ xS ][ yS ] && ( n >0 || !inferSbDcSigCoeffflag ) ) {     sig_coeff_flag[ xC ][ yC ] ae(v)    remBinsPass1 − −     if( sig eoeff flag[ xC ][ yC ])     inferSbDcSigCoeffFlag = 0    }    if( sig_coeff_flag[ xC ][ yC ]) {    numSigCoeff ||I     abs_level_gt1_flag[ n ] ae(v)     remBinsPass1−−     if( abs_level_gt1_flag[ n ]) {      par_level_flag[ n ] ae(v)     remBinsPass1− −      if( remBinsPass2 > 0) {       remBinsPass2− −      if( remBinsPass2 = = 0)        firstPosMode1 = n − 1      }     }    if( lastSigScanPosSb = = −1 )      lastSigScanPosSb = n    firstSigScanPosSb = n    }    AbsLevelPass1[ xC ][ yC ] =     sig_coeff_flag[ xC ][ yC ] + par_level_flag[ n ] +abs_level_gt1_flag[ n ]    if( dep_quant_enabled_flag)     QState =QStateTransTable[ QState ][ AbsLevelPass][ xC ][ yC ] & 1]    if(remBinsPass1 < 3 )     firstPosMode2 = n − 1   }   if( firstPosMode1 <firstPosMode2 )    firstPosMode1 = firstPosMode2   for( n = numSbCoeff −1; n >= firstPosMode2; n− −)    if( abs_level_gt1_flag[ n ])    abs_level_gt3_flag[ n ] ae(v)   for( n − numSbCoeff − 1; n >−firstPosMode1; n− − ) {    xC = ( xS << log2SbSize ) + DiagScanOrder[log2SbSize ][ log2SbSize ][ n ][ 0 ]    yC = ( yS << log2SbSize ) +DiagScanOrder[ log2SbSize ][ log2ShSize ][ n ][ 1 ]    if(abs_level_gt3_flag[ n ])     abs_remainder[ n ] ae(v)    AbsLevel[ xC ][yC ] = AbsLevelPassl xC ][ yC ] +          2 * ( abs level gt3 flag[ n] + abs remainder[ n ])   }   for( n = firstPosMode1; n > firstPosMode2;n − −) {    xC = ( xS << log2SbSize ) + DiagScanOrder[ log2SbSize ][log2SbSize ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + DiagScanOrder[log2SbSize ][ log2SbSize ][ n ][ 1 ]    if( abs_level_gt1_flag[ n ])    abs_remainder[ n ] ae(v)    AbsLevel[ xC ][ yC ] = AbsLevelPass1[ xC][ yC ] + 2 * abs remainder[ n ]   }   for( n − firstPosMode2; n >− 0; n− −) {    xC = ( xS << log2SbSize ) + DiagScanOrder[ log2SbSize ][log2SbSize ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + DiagScanOrder[log2SbSize ][ log2ShSize ][ n ][ 1 ]    dec abs level[ n ] ae(v)   if(AbsLevel[ xC ][ yC ] > 0 )     firstSigScanPosSb − n    if(dep_quant_enabled_flag)     QState − QStateTransTable[ QState][AbsLevel[ xC ][ yC ] & 1 ]   }   if( dep_quant_enabled_ ||!sign_data_hiding_enabled_flag )    signHidden = 0   else    signHidden= ( lastSigScanPosSb − firstSigScanPosSb >3 ? 1 : 0)   for( n =numSbCoeff − 1; n >= 0; n − − ) {    xC = ( xS << log2SbSize ) +DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]    yC = ( yS <<log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]   if( sig coeff flag[ xC ][ yC ] &&    ( !signHidden || ( n !=firstSigScanPosSb ) ) )     coeff sign flag[ n ] ae(v)   }   if( depquant enabled flag) {    QState = startQStateSb    for( n = numSbCoeff −1 n >= 0 ) {     xC = ( xS << log2SbSize ) +       DiagScanOrder[log2SbSize ][ log2SbSize ][ n ][ 0 ]     yC = ( yS << log2SbSize ) +      DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]     if( sigcoeff flag[ x ][ yC ] )      TransCoeffLevel x0 ][ y0 ][ cIdx ][ xC ][yC ] =        ( 2 * AbsLevel[ xC ][ yC ] − ( QState >1 ? 1 : 0 ) )*       ( 1 − 2 * coeff sign flag[ n ] )     QState = QStateTransTable[QState ][ par level flag[ n ] ]   } else {    sumAbsLevel = 0    for(n + numSbCoeff 1;n >= 0;n ) {     xC = ( xS << log2SbSize) +      DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]     yC = ( yS<< log2SbSize ) +       DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][1 ]     if( sig coeff flag[ xC ][ yC ] ) {      TransCoeffLevel[ x0 ][y0 ][ cIdx ][ xC ][ yC ] =        AbsLevel[ xC ][ yC ] * ( 1 − 2 * coeffsign flag[ n ] )      if( signHidden ) {       sumAbsLevel += AbsLevel[xC ][ yC ]       if( (n = = firstSigScanPosSb ) && ( sumAbsLevel % 2) == 1 ) )        TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =         −TransCoeffLevel[ x0 ][ y0 ][ cldx ][ xC ][ yC ]      }     }   }   }  }  if( tu mts flag[ x0 ][ y0 ] && ( cIdx = = 0 ) )   mts_idx[x0 ][ y0 ][cIdx ] ae(v) }

transform_skip_flag indicates whether transform is skipped in anassociated block. The transform_skip_flag may be a syntax element of atransform skip flag. The associated block may be a coding block (CB) ora transform block (TB). Regarding transform (and quantization) andresidual coding procedures, CB and TB may be used interchangeably. Forexample, as described above, residual samples may be derived for CB, and(quantized) transform coefficients may be derived through transform andquantization for the residual samples, and through the residual codingprocedure, information (e.g., syntax elements) efficiently indicating aposition, magnitude, sign, etc. of the (quantized) transformcoefficients may be generated and signaled. The quantized transformcoefficients may simply be called transform coefficients. In general,when the CB is not larger than a maximum TB, a size of the CB may be thesame as a size of the TB, and in this case, a target block to betransformed (and quantized) and residual coded may be called a CB or aTB. Meanwhile, when the CB is greater than the maximum TB, a targetblock to be transformed (and quantized) and residual coded may be calleda TB. Hereinafter, it will be described that syntax elements related toresidual coding are signaled in units of transform blocks (TBs) but thisis an example and the TB may be used interchangeably with coding blocks(CBs as described above.

Meanwhile, syntax elements which are signaled after the transform skipflag is signaled may be the same as the syntax elements disclosed inTable 2 below, and detailed descriptions on the syntax elements aredescribed below.

TABLE 2 transform unit( x0, y0, tbWidth, tbHeight, treeType, subTuIndex,chType ) { Descriptor  if( IntraSubPartitionsSplitType != ISP_NO_SPLIT&&    treeType = = SINGLE_TREE && subTuIndex = = NumIntraSubPartitions −1 ) {   xC = CbPosX[ chType ][ x0 ][ y0 ]   yC = CbPosY[ chType ][ x0 ][y0 ]   wC = CbWidth[ chType ][ x0 ][ y0 ] / SubWidthC   hC = CbHeight[chType ][ x0 ][ y0 ] / SubHeightC  } else {   xC = x0   yC = y0   wC =tbWidth / SubWidthC   hC = tbHeight / SubHeightC  }  chromaAvailable =treeType != DUAL_TREE_LUMA && sps_chroma_format_ idc !=0 &&   (IntraSubPartitionsSplitType = = ISP_NO_SPLIT ||   (IntraSubPartitionsSplitType != ISP_NO_SPLIT &&   subTuIndex = =NumIntraSubPartitions − 1 ) )  if( ( treeType = = SINGLE_TREE ||treeType = = DUAL_TREE_CHROMA) &&    sps_chroma_format_idc != 0 &&    (( intraSubPartitionsSplitType = = ISP_NO_SPLIT && !( cu_sbt_flag &&    (( subTuIndex = = 0 && cu_sbt_pos flag ) ||    ( subTuIndex = = 1 &&!cu_sbt_pos flag ) ) ) ) ||    ( IntraSubPartitionsSplitType !=ISP_NO_SPLIT &&    ( subTuIndex = = NumIntraSubPartitions − 1 ) ) ) ) {  tu_cb_coded_flag[ xC ][ yC ] ae (v)   tu_cr_coded_flag[ xC ][ yC ] ae(v)  }  if( treeType = = SINGLE TREE || treeType = = DUAL TREE LUMA ) {  if( ( IntraSubPartitionsSplitType = = 1SP_NO_SPL1T && !( cu_sbt_flag &&    ( ( subTuIndex = = 0 && cu_sbt_pos_flag ) ||    ( subTulndex = = 1&& !cu_sbt_pos_flag ) ) ) &&    ( ( CuPredMode[ chType ][ x0 ][ y0 ] = =MODE _INTRA &&    !cu_act_enabled_flag[ x0 ][ y0 ]) ||    (chromaAvailable && ( tu_cb_coded_flag[ xC ][ yC ] ||   tu_cr_coded_flag[ xC ][yC ] ) ) ||    CbWidth[ chType ][ x0 ][ y0 ] >MaxTbSizeY ||    CbHeight[_chType ][ x0 ][ y0 ] > MaxTbSizeY ) ) ||    (IntraSubPartitionsSplitType != ISP_NO_SPLIT &&    ( subTulndex <NumIntraSubPartitions − 1 || !InferTuCbfLuma ) ) )   tu_y_coded flag[ x0][ y0 ] ac(v)  if(IntraSubPartitionsSplitType !=ISP NO SPLIT)  InferTuCbfLuma = InferTuCbfLuma && !tu y coded flag[ x0 ][ y0 ]  } if( ( CbWidth[ chType ][ x0 ][ y0 ] > 64 || CbHeight[ chType ][ x0 ][y0 ] > 64 ||   tu_y_coded_flag[ x0 ][ y0 ] || ( chromaAvailable &&(tu_cb_coded_flag [ xC ][ yC ] ||   tu_cr_coded_flag[ xC ][ yC ] ) ) &&treeType != DUAL_TREE_CHROMA &&   pps_cu_qp_delta enabled flag &&!IsCuQpDeltaCoded ) {   cu_qp_delta_abs ae(v)   if( cu_qp_delta_abs)   cu_qp_delta_sign_flag ae(v)  }  if( ( CbWidth[ chType ][ x0 ][ y0 ] >64 || CbHcight[ chType ][ x0 ][ y0 ] > 64 ||    ( chromaAvailable && (tu_cb_coded_flag xC ][ YC ] ||    tu_cr_coded_flag [ xC ][ yC ] ) ) ) &&   treeType != DUAL_TREE_LUMA && sh_cu_chroma_qp_offset_enabled_ flag &&   !IsCuChromaQp0ffsetCoded ) {   cu_chroma_qp_offset_flag ae(v)   if(cu_chroma_qp_offset_flag && pps_chroma_qp_offset_list_len_minusl > 0)   cu_chroma_qp_offset_idx ae(v)  }  if( sps_joint_cbcr_enabledflag && (( CuPredMode[ chType ][ x0 ][ y0 ] = = MODE_INTRA    && (tu_cb_coded_flag[ xC ][ YC [ 1 ] tu_cr_coded_flag[ xC ][ YC [ ) ) 1 1   ( tu_cb_coded_flag[ xC ][ yC ]&& tu_cr_coded_flag+ xC ][ yC ]) ) &&   chromaAvailable )   tu _joint_cbcr_residual flag[xC ][ yC ] ae(v) if( tu y coded flag[ x0 ][ y0 ] && treeType != DUAL TREE CHROMA ) {  if( sps_transform_skip_enabled_flag && !BdpcmFlag[ x0 ][ y0 ][ 0 ] &&    tbWidth <= MaxTsSize && tbHeight <= MaxTsSize &&     (IntraSubPartitionsSplitType = = ISP_NO_SPLIT) && !cu sbt flag)   transform_skip_flag[ x0 ][ y0 ][ 0 ] ae(v)   if(!transform_skip_flag[ x0 ][ y0 ][ 1 ] || sh_ts_residual_coding_disabled_flag )    residual coding( x0, y0, Log2( tbWidth ), Log2( tbHcight ), 0)  else    residual_ts_coding( x0, y0, Log2( tbWidth ), Log2( tbHeight ),0)  if( tu_cb_coded_flag[ xC ][ yC ] && treeType != DUAL TREE LUMA ) {  if( sps_transform_skip_enabled_flag && !BdpcmFlag[ x0 ][ y0 ][ 1 ] &&    wC <= MaxTsSize && hC <= MaxTsSize && !cu sbt flag)    transformskip flag[ xC ][ yC ][ 1 ] ae(v)   if( !transform skip flag[ xC ][ yC ][1 ] || sh_ts_residual_coding_disabled_ flag )   residual coding( xC, yC,Log2( wC ), Log2( hC), 1)  else   residual ts coding( xC, yC, Log2( wC), Log2( hC), 1)  }  if( tu_cr_coded flag[ xC ][ yC ] && treeType !=DUAL_TREE_LUMA &&    !( tu_cb_codcd_flag[ xC ][ yC ] &&tu_joint_cbcr_residual_flag[ xC ][ yC ] ) ) {  if(sps_transform_skip_enabled_flag && !BdpcmFlag[ x0 ][ y0 ][ 2 ] &&    wC<= MaxTsSize && hC <= MaxTsSize && !cu sbt flag)    transform skip flag[xC ][ yC ][ 2 ] ae(v)   if( !transform_skip_flag[ xC ][ yC ][ 2 ] ||sh_ts_residual_coding_disabled_ flag )    residual coding( xC, yC, Log2(wC ), Log2( hC), 2)   else    residual ts coding( xC, yC, Log2( wC ),Log2( hC), 2)  } }

TABLE 3 residual coding( x0, y0, log2TbWidth, log2TbHeight, cIdx ) 1Descriptor  if( sps_mts_enabled_flag && cu_sbt_flag && cldx = = 0 &&   log2TbWidth = = 5 && log2TbHeight < 6)   log2ZoTbWidth = 4  else  log2ZoTbWidth = Min( log2TbWidth, 5)  if( sps_mts_enabled_flag &&cu_sbt_flag && cIdx = = 0 &&    log2TbWidth < 6 && log2TbHeight = = 5)  log2ZoTbHeight = 4  else   log2ZoTbHeight = Min( log2TbHeight, 5)  if(log2TbWidth > 0)   last sig coeff x prefix ae(v)  if( log2TbHeight > 0)  last sig coeff y prefix ae(v)  if( last sig coeff x prefix > 3)   lastsig coeff x suffix ae(v)  if( last sig coeff y prefix > 3)  last sigcoeff y suffix ae(v)  log2TbWidth = log2ZoTbWidth  log2TbHeight =log2ZoTbHeight  remBinsPass 1 = ( ( 1 << ( log2TbWidth + log2TbHeight )) * 7) >> 2  log2SbW = ( Min( log2TbWidth, log2TbHeight) < 2 ? 1 : 2) log2SbH = log2SbW  if( log2TbWidth + log2TbHeight > 3)   if(log2TbWidth < 2) 1    log2SbW = log2TbWidth    log2SbH = 4 − log2SbW   }else if( log2TbHeight < 2) {    log2SbH = log2TbHeight    log2SbW = 4 −log2SbH   }  numSbCoeff = 1 << ( log2SbW + log2SbH)  lastScanPos =numSbCoeff  lastSubBlock = ( 1 << ( log2TbWidth + log2TbHeight − (log2SbW + log2Sb H ) ) ) − 1  do {   if( lastScanPos = = 0) {   lastScanPos = numSbCoeff    lastSubBlock − −   }   lastScanPos − −  xS = DiagScanOrder[ log2TbWidth − log2SbW ][ log2TbHeight − log2SbH ]      [ lastSubBlock ][ 0 ]   yS = DiagScanOrder[ log2TbWidth − log2SbW][ log2TbHeight − log2SbH ]       [ lastSubBlock ][ 1 ]   xC = ( xS <<log2SbW ) + DiagScanOrder[ log2SbW ][ log2SbH ][ lastScan Pos ][ 0 ]  yC = ( yS << log2SbH ) + DiagScanOrder[ log2SbW ][ log2SbH ][ lastScanPos ][ 1 ]  } while( ( xC != LastSignificantCoeffX ) || ( yC !=LastSignificantCoeffY ) )  if( lastSubBlock = = 0 && log2TbWidth >=2 &&log2TbHeight >=2 & &    !transform_skip_flag[ x0 ][ y0 ][ cIdx ] &&lastScanPos > 0)   LfnstDcOnly = 0  if( ( lastSubBlock > 0 &&log2TbWidth >=2 && log2TbHeight >=2) ||    ( lastScanPos > 7 && (log2TbWidth = = 2 1 1 log2TbWidth ==3) & &    log2TbWidth ==log2TbHeight ) )   LfnstZeroOutSigCoeffFlag = 0  if( ( lastSubBlock > 0|| lastScanPos > 0) && cIdx = = 0)   MtsDcOnly = 0  QState = 0  for( i =lastSubBlock; i >= 0; i − −) {   startQStateSb = QState   xS =DiagScanOrder[ log2TbWidth − log2SbW ][ log2TbHeight − log2SbH ]       [i ][ 0 ]   yS = DiagScanOrder[ log2TbWidth − log2SbW ][ log2TbHeight −log2SbH ]       [ i ][ 1 ]   inferSbDcSigCoeffFlag = 0   if( i <lastSubBlock && i > 0) {    sb coded flag[ xS ][ yS ] ae(v)   inferSbDcSigCoeffFlag = 1   }   if( sb coded flag[ xS 1[ yS ] && (xS > 3 || yS > 3) && cIdx = = 0)    MtsZeroOutSigCoeffFlag = 0  firstSigScanPosSb = numSbCoeff   lastSigScanPosSb = −1   firstPosMode0= ( i = = lastSubBlock ? lastScanPos : numSbCoeff − 1)   firstPosMode 1= firstPosMode0   for( n = firstPosMode0; n >= 0 && remBinsPass 1 >= 4;n− −) {    xC = ( xS << log2SbW ) +DiagScanOrder + log2SbW ][ log2SbH ][n ] [ 0 ]    yC = ( yS << log2SbH ) + DiagScanOrder + log2SbW ][ log2SbH][ n ] [ 1 ]    if( sb_coded_flag[ xS ][ yS ] && ( n > 0 ||!inferSbDcSigCoeffFlag ) & &       ( xC != LastSignificantCoeffX || yC!= Last SignificantCoeffY ) ) {     sig coeff flag[xC ][ yC ] ae(v)    remBinsPass1− −     if( sig coeff flag[ xC ][ yC ] )     inferSbDcSigCoeffFlag = 0    }    if( sig_coeff_flag[ xC ][ yC ] ){     abs level gtx flag[ n ][ 0 ] ae(v)     remBinsPass1− −     if( abslevel gtx flag[ n ][ 0 ] ) {      par_level_flag[ n ] ae(v)     remBinsPass1− −      abs level gtx flag[ n ][ 1 ] ae(v)     remBinsPass1− −     }     if( lastSigScanPosSb = = −1)     lastSigScanPosSb = n     firstSigScanPosSb = n    }   AbsLevelPass1 [ xC ][ yC ] = sig coeff flag[ xC ][ yC ] +par_level_flag [ n ] +       abs_level_gtx_flag[ n ] [ 0 ] + 2 *abs_level_gtx_flag[ n ] [ 1 ]    if( sh_dep_quant_used_flag)     QState= QStateTransTable[ QState ][ AbsLevelPass ][ xC ][ yC ] & 1 ]   firstPosMode1 = n − 1   }   for( n = firstPosMode0; n > firstPosMode1; n− −) {    xC = ( xS << log2SbW) + DiagScanOrder[ log2SbW ][ log2SbH][ n ] [ 0 1    yC = ( yS << log2SbH) + DiagScanOrder[ log2SbW ][log2SbH ][ n ] [ 1 ]    if( abs_level_gtx_flag[ n ][ 1 ] )    abs_remainder[ n ] ae(v)    AbsLevel [ xC ][ yC ] = AbsLevelPass1[xC ][ yC ] + 2 * abs remainder[ n ]   }   for( n = firstPosMode1; n >=0;n− −) {    xC = ( xS << log2SbW) + DiagScanOrder[ log2SbW ][ log2SbH ][n ] [ 0 ]    yC = ( yS << log2SbH) + DiagScanOrder[ log2SbW ] [ log2SbH][ n ] [ 1 ]    if( sb_coded_flag[ xS ][ yS ] )     dec_abs_level[ n ]ae(v)    if( AbsLevel[ xC ][ yC ] > 0) {     if( lastSigScanPosSb = =−1)      lastSigScanPosSb = n     firstSigScanPosSb = n    }    if(sh_dep_quant_used_flag)     QState = QStateTransTable[ QState ][AbsLevel[ xC ][ yC ] & 1 ]   }   if( sh_dep_quant_used_flag ||!sh_sign_data_hiding_used_flag)    signHidden = 0   else    signHidden =( lastSigScanPosSb − firstSigScanPosSb >3 ? 1 : 0 )   for( n =numSbCoeff − 1; n >= 0; n− −) {    xC = ( xS << log2SbW ) +DiagScanOrder[ log2SbW ][ log2SbH ][ n ] [ 0 ]    yC = ( yS << log2SbH) + DiagScanOrder[ log2SbW ][ log2SbH][ n ] [ 1 ]    if( ( AbsLeyel[ xC][ yC ] > 0) &&     ( !signHidden || ( n != firstSigScanPosSb ) ) )    coeff_sign_flag[ n ] ae(v)   }   if( sh_dep_quant_used_flag) {   QState = startQStateSb    for( n = numSbCoeff − 1 n >= 0; n− − ) 1    xC = ( xS << log2SbW ) + DiagScanOrder + log2SbW ][ log2SbH ][ n ] [0 ]     yC = ( yS << log2SbH) + DiagScanOrdcr + log2SbW ][ log2SbH ][ n] [ 1 ]     if( AbsLeyel[ xC ][ yC ] > 0)      TransCoeffLevel[ x0 ][ y0][ cIdx [ xC ][ yC ] =        ( 2 * AbsLevel[ xC ][ yC ] − ( QState > 1? 1 : 0 ) ) *        ( 1 − 2 * coeff sign flag[ n ])     QState =QStateTransTable[ QState ][ AbsLevel[ xC ][ yC ] & 1 ]   } else {   sumAbsLevel = 0    for( n = numSbCoeff − 1; n >=0; n− − ) {     xC =( xS << log2SbW ) + DiagScanOrder + log2SbW ][ log2SbH ][ n ] [ 0 ]    yC = ( yS << log2SbH) + DiagScanOrder + log2SbW ][ log2SbH ][ n ] [1]     if( AbsLevel[ xC ][ yC ] > 0) {      TransCoeffLevel[ x0 ][ y0 ][cIdx [ xC ][ yC ] =        AbsLevel[ xC ][ yC ] * ( 1 − 2 *coeff_sign_flag[ n ])      if( signHidden ) {       sumAbsLeyel +=AbsLevel[ xC ][ yC ]       if( ( n = = firstSigScanPosSb ) && (sumAbsLeyel % 2) = = 1) )        TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC][ yC ] =          −TransCoeffLevel[ x0 ][ y0 ][ cIdx [ xC ][ yC ]     }     }    }   }  } }

TABLE 4 residual ts coding( x0, y0, 1og2TbWidth, log2TbHeight, cIdx ) {Descriptor  log2SbW = ( Min( log2TbWidth, 1og2TbHeight ) < 2 ? 1 : 2) log2SbH =1og2SbW  if( 1og2TbWidth + log2TbHeight > 3)   if( log2TbWidth< 2) {    log2SbW =1og2TbWidth    log2SbH =4 − log2SbW   } else if(1og2TbHeight < 2) {    log2SbH = 1og2TbHeight    log2SbW =4 − log2SbH  }  numSbCoeff = 1 << (log2SbW + log2SbH)  lastSubBlock = ( 1 << (log2TbWidth +1og2TbHeight − ( log2SbW + log2Sb H ) ) ) − 1  inferSbCbf =1  RemCcbs = ( ( 1 << ( log2TbWidth + log2TbHeight ) ) * 7) >> 2  for( i=0; i <= lastSubBlock; i++) {   xS = DiagScanOrder[ 1og2TbWidth −log2SbW ][ 1og2TbHeight − 1og2SbH ] [ i ][ 0 ]   yS = DiagScanOrder[1og2TbWidth − log2SbW ][ 1og2TbHeight − 1og2SbH ] [ i ][ 1 ]   if( i !=lastSubBlock || !inferSbCbf )    sb_coded _lag[ xS ][ yS ] ae(v)   if(sb coded flag[ xS ][ yS ] && i <lastSubBlock )    inferSbCbf = 0  /*First scan pass */   inferSbSigCoeffFlag = 1   lastScanPosPass 1 = −1  for( n = 0; n <= numSbCoeff − 1 && RemCcbs >= 4; n++ ) {    xC = ( xS<< log2SbW) + DiagScanOrder[ 1og2SbW ][ 1og2SbH ][ n ] [ 0 ]    yC = (yS << log2SbH ) + DiagScanOrder[ log2SbW ][ 1og2SbH ][ n ] [ 1 ]   lastScanPosPass1 = n    if( sb_coded_flag[ xS ][ yS ] &&      ( n !=numSbCoeff − || !inferSbSigCoeffflag ) ) {     sig_coeff_flag[ xC ][ yC] ae(v)     RemCcbs− −     if( sig_coeff_flag[ xC ][ yC ])     inferSbSigCoeffflag = 0    }    CoeffSignLevel[ xC ][ yC ] = 0   if( sig coeff flag[ xC ][ yC ]) {     coeff sign flag[ n ] ae(v)    RemCcbs− −     CoeffSignLevel[ xC ][ yC ] = ( coeff sign flag[ n ] >0 ? −1 : 1)     abs_level_gtx_flag[ n ][ 0 ] ae(v)     RemCcbs− −    if( abs_level_gtx_flag[ n ][ 0 ]) {      par_level_flag[ n ] ae(v)     RemCcbs− −     }    }    AbsLevelPass1[ xC ][ yC ] =     sig_coeff_flag[ xC ][ yC ] + par_level_flag[ n ] +abs_level_gtx_flag [ n ][ 0 ]   }  /* Greater than X scan pass(numGtXFlags=5) */   lastScanPosPass2 = −1   for( n = 0; n <= numSbCocff− 1 && RemCcbs >= 4; n++ ) {    xC = ( xS << log2SbW ) + DiagScanOrder[log2SbW ][ log2SbH ][ n ] [ 0 ]    yC = ( yS << 1og2SbH ) +DiagScanOrdcr[ log2SbW ][ log2SbH ][ n ] [ 1 ]    AbsLevelPass2[ xC ][yC ] = AbsLevelPass1 [ xC ][ yC ]    for( j = 1; j < 5; j++ ) {     if(abs_level_gtx flag[ n ][ j − 1 ] ) {     abs_level_gtx_flag[ n ][ j ]ac(v)     RemCcbs− −    }    AbsLevelPass2[ xC ][ yC ] += 2 * abs levelgtx flag[ n ][ j ]   }   lastScanPosPass2 = n  }  /* remainder scan pass*/   for( n = 0; n <= numSbCoeff − 1; n++ ) {    xC = ( xS << 1og2SbW) + DiagScanOrder[ log2SbW ][ log2SbH ][ n ] [ 0 ]    yC = ( yS <<1og2SbH ) + DiagScanOrder[ 1og2SbW ][ log2SbH ][ n ] [ 1 ]    if( ( n <=lastScanPosPass2 && AbsLeve1Pass2[ xC ][ yC ] >= 10) ||      ( n >lastScanPosPass2 && n <= lastScanPosPass1 &&      AbsLevelPass1[ xC ][yC ] >= 2) ||      ( n > lastScanPosPass1 && sb_coded_flag[ xS ][ yS ] ))     abs remainder[ n ] ae(v)    if( n <= lastScanPosPass2)    AbsLevel[ xC ][ yC ] = AbsLevelPass2[ xC ][ yC ] + 2 * abs_remainder[ n ]    else if(n <= lastScanPosPass1 )     AbsLevel[ xC ][ yC ] =AbsLevelPass1[ xC ][ yC ] + 2 * abs_remainder [ n ]    else { /* bypass*/     AbsLevel[ xC ][ yC ] = abs_remainder[ n ]     if( abs_remainder[n ] )      coeff sign flag[ n ] ae(v)    }    if( BdpcmFlag[ x0 ][ y0 ][cIdx ] = = 0 && n <= lastScanPosPass1 ) {     absLeftCoeff = xC > 0 ?AbsLevel[ xC ][ 1 ][ yC ]) : 0     absAboveCoeff = yC > 0 ? AbsLevel[ xC][ yC − 1 ] ) : 0     predCoeff = Max( absLeftCoeff, absAboveCoeff )    if( AbsLevel[ xC ][ yC ] = = 1 && predCoeff > 0)      AbsLevel[ xC][ yC ] = predCoeff     else if( AbsLevel[ xC ][ yC ] > 0 && AbsLevel[xC ][ yC ] <= predCoeff )      AbsLevel[ xC ][ yC ]− −    }   TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] = ( 1 − 2 * coeffsign_flag [ n ] ) *      AbsLevel[ xC ][ yC ]   }  } }

According to the present embodiment, as shown in Table 2, residualcoding may be divided according to a value of the syntax elementtransform_skip_flag of the transform skip flag. That is, a differentsyntax element may be used for residual coding based on the value of thetransform skip flag (based on whether the transform is skipped).Residual coding used when the transform skip is not applied (that is,when the transform is applied) may be called regular residual coding(RRC), and residual coding used when the transform skip is applied (thatis, when the transform is not applied) may be called transform skipresidual coding (TSRC). Also, the regular residual coding may bereferred to as general residual coding. Also, the regular residualcoding may be referred to as a regular residual coding syntax structure,and the transform skip residual coding may be referred to as a transformskip residual coding syntax structure. Table 3 above may show a syntaxelement of residual coding when a value of transform_skip_flag is 0,that is, when the transform is applied, and Table 4 above may show asyntax element of residual coding when the value of transform_skip_flagis 1, that is, when the transform is not applied.

Specifically, for example, the transform skip flag indicating whether toskip the transform of the transform block may be parsed, and whether thetransform skip flag is 1 may be determined. If the value of thetransform skip flag is 0, as shown in Table 3, syntax elementslast_sig_coeff_x_prefix, last_sig_coeff_y_prefix,last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, sb_coded_flag,sig_coeff_flag, abs_level_gtx_flag, par_level_flag, abs_remainder,coeff_sign_flag and/or dec_abs_level for a residual coefficient of thetransform block may be parsed, and the residual coefficient may bederived based on the syntax elements. In this case, the syntax elementsmay be sequentially parsed, and a parsing order may be changed. Inaddition, the abs_level_gtx_flag may represent abs_level_gt1_flag,and/or abs_level_gt3_flag. For example, abs_level_gtx_flag[n][0] may bean example of a first transform coefficient level flag(abs_level_gt1_flag), and the abs_level_gtx_flag[n][1] may be an exampleof a second transform coefficient level flag (abs_level_gt3_flag).

Referring to the Table 3 above, last_sig_coeff_x_prefix,last_sig_coeff_y_prefix, last_sig_coeff_x_suffix,last_sig_coeff_y_suffix, sb_coded_flag, sig_coeff_flag,abs_level_gt1_flag, par_level_flag, abs_level_gt3_flag, abs_remainder,coeff_sign_flag, and/or dec_abs_level may be encoded/decoded. Meanwhile,sb_coded_flag may be represented as coded_sub_block_flag.

In an embodiment, the encoding apparatus may encode (x, y) positioninformation of the last non-zero transform coefficient in a transformblock based on the syntax elements last_sig_coeff_x_prefix,last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, andlast_sig_coeff_y_suffix. More specifically, the last_sig_coeff_x_prefixrepresents a prefix of a column position of a last significantcoefficient in a scanning order within the transform block, thelast_sig_coeff_y_prefix represents a prefix of a row position of thelast significant coefficient in the scanning order within the transformblock, the last_sig_coeff_x_suffix represents a suffix of a columnposition of the last significant coefficient in the scanning orderwithin the transform block, and the last_sig_coeff_y_suffix represents asuffix of a row position of the last significant coefficient in thescanning order within the transform block. Here, the significantcoefficient may represent a non-zero coefficient. In addition, thescanning order may be a right diagonal scanning order. Alternatively,the scanning order may be a horizontal scanning order or a verticalscanning order. The scanning order may be determined based on whetherintra/inter prediction is applied to a target block (a CB or a CBincluding a TB) and/or a specific intra/inter prediction mode.

Thereafter, the encoding apparatus may divide the transform block into4×4 sub-blocks, and then indicate whether there is a non-zerocoefficient in the current sub-block using a 1-bit syntax elementcoded_sub_block_flag for each 4×4 sub-block.

If a value of coded_sub_block_flag is 0, there is no more information tobe transmitted, and thus, the encoding apparatus may terminate theencoding process on the current sub-block. Conversely, if the value ofcoded_sub_block_flag is 1, the encoding apparatus may continuouslyperform the encoding process on sig_coeff_flag. Since the sub-blockincluding the last non-zero coefficient does not require encoding forthe coded_sub_block_flag and the sub-block including the DC informationof the transform block has a high probability of including the non-zerocoefficient, coded_sub_block_flag may not be coded and a value thereofmay be assumed as 1.

If the value of coded_sub_block_flag is 1 and thus it is determined thata non-zero coefficient exists in the current sub-block, the encodingapparatus may encode sig_coeff_flag having a binary value according to areverse scanning order. The encoding apparatus may encode the 1-bitsyntax element sig_coeff_flag for each transform coefficient accordingto the scanning order. If the value of the transform coefficient at thecurrent scan position is not 0, the value of sig_coeff_flag may be 1.Here, in the case of a subblock including the last non-zero coefficient,sig_coeff_flag does not need to be encoded for the last non-zerocoefficient, so the coding process for the sub-block may be omitted.Level information coding may be performed only when sig_coeff_flag is 1,and four syntax elements may be used in the level information encodingprocess. More specifically, each sig_coeff_flag[xC][yC] may indicatewhether a level (value) of a corresponding transform coefficient at eachtransform coefficient position (xC, yC) in the current TB is non-zero.In an embodiment, the sig_coeff_flag may correspond to an example of asyntax element of a significant coefficient flag indicating whether aquantized transform coefficient is a non-zero significant coefficient.

A level value remaining after encoding for sig_coeff_flag may be derivedas shown in the following equation. That is, the syntax elementremAbsLevel indicating a level value to be encoded may be derived fromthe following equation.

remAbsLevel=|coeff|−1  [Equation 1]

Herein, coeff means an actual transform coefficient value.

Additionally, abs_level_gt1_flag may indicate whether or notremAbsLevel’ of the corresponding scanning position (n) is greaterthan 1. For example, when the value of abs_level_gt1_flag is 0, theabsolute value of the transform coefficient of the correspondingposition may be 1. In addition, when the value of the abs_level_gt1_flagis 1, the remAbsLevel indicating the level value to be encoded later maybe updated as shown in the following equation.

remAbsLevel=remAbsLevel−1  [Equation 2]

In addition, the least significant coefficient (LSB) value ofremAbsLevel described in Equation 2 described above may be encoded as inEquation 3 below through par_level_flag.

par_level_flag=|coeff|& 1  [Equation 3]

Herein, par_level_flag[n] may indicate a parity of a transformcoefficient level (value) at a scanning position n.

A transform coefficient level value remAbsLevel that is to be encodedafter performing par_level_flag encoding may be updated as shown belowin the following equation.

remAbsLevel=remAbsLevel>>1  [Equation 4]

abs_level_gt3_flag may indicate whether or not remAbsLevel’ of thecorresponding scanning position (n) is greater than 3. Encoding forabs_remainder may be performed only in a case where rem_abs_gt3_flag isequal to 1. A relationship between the actual transform coefficientvalue coeff and each syntax element may be as shown below in thefollowing equation.

|coeff|=sig_coeff_flag+abs_level_gt1_flag+par_level_flag+2*(abs_level_gt3_flag+abs_remainder)  [Equation5]

Additionally, the following table indicates examples related to theabove-described Equation 5.

TABLE 5 |coeff[n]| sig_coeff_flag[n] abs_level_gtX_flag[n][0]par_level_flag[n] abs_level_gtX_flag[n][1] abs_remainder[n] 0 0 1 1 0 21 1 0 0 3 1 1 1 0 4 1 1 0 1 0 5 1 1 1 1 0 6 1 1 0 1 1 7 1 1 1 1 1 8 1 10 1 2 9 1 1 1 1 2 10 1 1 0 1 3 11 1 1 1 1 3 . . . . . . . . . . . .

Herein, |coeff| indicates a transform coefficient level (value) and mayalso be indicates as an AbsLevel for a transform coefficient.Additionally, a sign of each coefficient may be encoded by usingcoeff_sign_flag, which is a 1-bit symbol.

Also, if the value of the transform skip flag is 1, as shown in Table 4,syntax elements sb_coded_flag, sig_coeff_flag, coeff_sign_flag,abs_level_gtx_flag, par_level_flag and/or abs_remainder for a residualcoefficient of the transform block may be parsed, and the residualcoefficient may be derived based on the syntax elements. In this case,the syntax elements may be sequentially parsed, and a parsing order maybe changed. In addition, the abs_level_gtx_flag may representabs_level_gt1_flag, abs_level_gt3_flag, abs_level_gt5_flag,abs_level_gt1_flag, and/or abs_level_gt9_flag. For example,abs_level_gtx_flag[n][j] may be a flag indicating whether an absolutevalue or a level (a value) of a transform coefficient at a scanningposition n is greater than (j<<1)+1. The condition (j<<1)+1 may beoptionally replaced with a specific threshold such as a first threshold,a second threshold, or the like.

Meanwhile, CABAC provides high performance, but disadvantageously haspoor throughput performance. This is caused by a regular coding engineof the CABAC. Regular encoding (i.e., coding through the regular codingengine of the CABAC) shows high data dependence since it uses aprobability state and range updated through coding of a previous bin,and it may take a lot of time to read a probability interval anddetermine a current state. The throughput problem of the CABAC may besolved by limiting the number of context-coded bins. For example, asshown in Table 1 or Table 3 described above, a sum of bins used toexpress sig_coeff_flag, abs_level_gt1_flag, par_level_flag, andabs_level_gt3_flag may be limited to the number of bins depending on asize of a corresponding block. Also, for example, as shown in Table 4described above, a sum of bins used to express sig_coeff_flag,coeff_sign_flag, abs_level_gt1_flag, par_level_flag, abs_level_gt3_flagabs_level_gt5_flag, abs_level_gt7_flag, abs_level_gt9_flag may belimited to the number of bins depending on a size of a correspondingblock. For example, if the corresponding block is a block of a 4×4 size,the sum of bins for the sig_coeff_flag, abs_level_gt1_flag,par_level_flag, abs_level_gt3_flag or sig_coeff_flag, coeff_sign_flag,abs_level_gt1_flag, par_level_flag, abs_level_gt3_flagabs_level_gt5_flag, abs_level_gt7_flag, abs_level_gt9_flag may belimited to 32 (or ex. 28), and if the corresponding block is a block ofa 2×2 size, the sum of bins for the sig_coeff_flag, abs_level_gt1_flag,par_level_flag, abs_level_gt3_flag may be limited to 8 (or ex. 7). Thelimited number of bins may be represented by remBinsPass1 or RemCcbs.Or, for example, for higher CABAC throughput, the number of contextcoded bins may be limited for a block (CB or TB) including a codingtarget CG. In other words, the number of context coded bins may belimited in units of blocks (CB or TB). For example, when the size of thecurrent block is 16×16, the number of context coded bins for the currentblock may be limited to 1.75 times the number of pixels of the currentblock, i.e., 448, regardless of the current CG.

In this case, if all context-coded bins of which the number is limitedare used when a context element is coded, the encoding apparatus maybinarize the remaining coefficients through a method of binarizing thecoefficient as described below, instead of using the context coding, andmay perform bypass encoding. In other words, for example, if the numberof context-coded bins which are coded for 4×4 CG is 32 (or ex. 28), orif the number of context-coded bins which are coded for 2×2 CG is 8 (orex. 7), sig_coeff_flag, abs_level_gt1_flag, par_level_flag,abs_level_gt3_flag which are coded with the context-coded bin may nolonger be coded, and may be coded directly to dec_abs_level. Or, forexample, when the number of context coded bins coded for a 4×4 block is1.75 times the number of pixels of the entire block, that is, whenlimited to 28, the sig_coeff_flag, abs_level_gt1_flag, par_level_flag,and abs_level_gt3_flag coded as context coded bins may not be coded anymore, and may be directly coded as dec_abs_level as shown in Table 6below.

TABLE 6 |coeff[n]| dec_abs_level[n] 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 89 9 10 10 11 11 . . . . . .

A value |coeff| may be derived based on dec_abs_level. In this case, atransform coefficient value, i.e., |coeff|, may be derived as shown inthe following equation.

|coeff|=dec_abs_level  [Equation 6]

In addition, the coeff_sign_flag may indicate a sign of a transformcoefficient level at a corresponding scanning position n. That is, thecoeff_sign_flag may indicate the sign of the transform coefficient atthe corresponding scanning position n.

FIG. 8 shows an example of transform coefficients in a 4×4 block.

The 4×4 block of FIG. 8 represents an example of quantized coefficients.The block of FIG. 8 may be a 4×4 transform block, or a 4×4 sub-block ofan 8×8, 16×16, 32×32, or 64×64 transform block. The 4×4 block of FIG. 8may represent a luma block or a chroma block.

Meanwhile, as described above, when an input signal is not a binaryvalue but a syntax element, the encoding apparatus may transform theinput signal into a binary value by binarizing a value of the inputsignal. In addition, the decoding apparatus may decode the syntaxelement to derive a binarized value (e.g., a binarized bin) of thesyntax element, and may de-binarize the binarized value to derive avalue of the syntax element. The binarization process may be performedas a truncated rice (TR) binarization process, a k-th order Exp-Golomb(EGk) binarization process, a limited k-th order Exp-Golomb (limitedEGk), a fixed-length (FL) binarization process, or the like. Inaddition, the de-binarization process may represent a process performedbased on the TR binarization process, the EGk binarization process, orthe FL binarization process to derive the value of the syntax element.

For example, the TR binarization process may be performed as follows.

An input of the TR binarization process may be cMax and cRiceParam for asyntax element and a request for TR binarization. In addition, an outputof the TR binarization process may be TR binarization for symbolValwhich is a value corresponding to a bin string.

Specifically, for example, in the presence of a suffix bin string for asyntax element, a TR bin string for the syntax element may beconcatenation of a prefix bin string and the suffix bin string, and inthe absence of the suffix bin string, the TR bin string for the syntaxelement may be the prefix bin string. For example, the prefix bin stringmay be derived as described below.

A prefix value of the symbolVal for the syntax element may be derived asshown in the following equation.

prefixVal=symbolVal>>cRiceParam  [Equation 7]

Herein, prefixVal may denote a prefix value of the symbolVal. A prefix(i.e., a prefix bin string) of the TR bin string of the syntax elementmay be derived as described below.

For example, if the prefixVal is less than cMax>>cRiceParam, the prefixbin string may be a bit string of length prefixVal+1, indexed by binIdx.That is, if the prefixVal is less than cMax>>cRiceParam, the prefix binstring may be a bit string of which the number of bits is prefixVal+1,indicated by binIdx. A bin for binIdx less than prefixVal may be equalto 1. In addition, a bin for the same binIdx as the prefixVal may beequal to 0.

For example, a bin string derived through unary binarization for theprefixVal may be as shown in the following table.

TABLE 7 prefixVal Bin string 0 0 1 1 0 2 1 1 0 3 1 1 1 0 4 1 1 1 1 0 5 11 1 1 1 0 . . . binIdx 0 1 2 3 4 5

Meanwhile, if the prefixVal is not less than cMax>>cRiceParam, theprefix bin string may be a bit string in which a length iscMax>>cRiceParam and all bits are 1.

In addition, if cMax is greater than symbolVal and if cRiceParam isgreater than 0, a bin suffix bin string of a TR bin string may bepresent. For example, the suffix bin string may be derived as describedbelow.

A suffix value of the symbolVal for the syntax element may be derived asshown in the following equation.

suffixVal=symbolVal−((prefixVal)<<cRiceParam)  [Equation 8]

Herein, suffixVal may denote a suffix value of the symbolVal.

A suffix of a TR bin string (i.e., a suffix bin string) may be derivedbased on an FL binarization process for suffixVal of which a value cMaxis (1<<cRiceParam)−1.

Meanwhile, if a value of an input parameter, i.e., cRiceParam, is 0, theTR binarization may be precisely truncated unary binarization, and mayalways use the same value cMax as a possible maximum value of a syntaxelement to be decoded.

In addition, for example, the EGk binarization process may be performedas follows. A syntax element coded with ue(v) may be a syntax elementsubjected to Exp-Golomb coding.

For example, a 0-th order Exp-Golomb (EGO) binarization process may beperformed as follows.

A parsing process for the syntax element may begin with reading a bitincluding a first non-zero bit starting at a current position of abitstream and counting the number of leading bits equal to 0. Theprocess may be represented as shown in the following table.

TABLE 8 leadingZeroBits = −1 for( b = 0; !b; leadingZeroBits++ )   b =read_bits( 1 )

In addition, a variable ‘codeNum’ may be derived as shown in thefollowing equation.

codeNum=2^(leadingZeroBits)−1+read_bits(leadingZeroBits)  [Equation 9]

Herein, a value returned from read_bits(leadingZeroBits), that is, avalue indicated by read_bits(leadingZeroBits), may be interpreted asbinary representation of an unsigned integer for a most significant bitrecorded first.

A structure of an Exp-Golomb code in which a bit string is divided intoa “prefix” bit and a “suffix” bit may be represented as shown in thefollowing table.

TABLE 9 Bit string form Range of codeNum 1 0 0 1 x₀ 1 . . . 2 0 0 1 x₁x₀ 3 . . . 6 0 0 0 1 x₂ x₁ x₀  7 . . . 14 0 0 0 0 1 x₃ x₂ x₁ x₀ 15 . . .30 0 0 0 0 0 1 x₄ x₃ x₂ x₁ x₀ 31 . . . 62 . . . . . .

The “prefix” bit may be a bit parsed as described above to calculateleadingZeroBits, and may be represented by 0 or 1 of a bit string inTable 9. That is, the bit string disclosed by 0 or 1 in Table 9 abovemay represent a prefix bit string. The “suffix” bit may be a bit parsedin the computation of codeNum, and may be represented by xi in Table 9above. That is, a bit string disclosed as xi in Table 9 above mayrepresent a suffix bit string. Herein, i may be a value in the range ofLeadingZeroBits-1. In addition, each xi may be equal to 0 or 1.

A bit string assigned to the codeNum may be as shown in the followingtable.

TABLE 10 Bit string codeNum 1 0 0 1 0 1 0 1 1 2 0 0 1 0 0 3 0 0 1 0 1 40 0 1 1 0 5 0 0 1 1 1 6 0 0 0 1 0 0 0 7 0 0 0 1 0 0 1 8 0 0 0 1 0 1 0 9. . . . . .

If a descriptor of the syntax element is ue(v), that is, if the syntaxelement is coded with ue(v), a value of the syntax element may be equalto codeNum.

In addition, for example, the EGk binarization process may be performedas follows.

An input of the EGk binarization process may be a request for EGkbinarization. In addition, the output of the EGk binarization processmay be EGk binarization for symbolVal, i.e., a value corresponding to abin string.

A bit string of the EGk binarization process for symbolVal may bederived as follows.

TABLE 11 absV = Abs( symbolVal ) stopLoop = 0 do   if( absV >= ( 1 << k) ) {     put( 1 )     absV = absV − ( 1 << k )     k++   } else {    put( 0 )     while( k− − )       put( ( absV >> k) & 1)     stopLoop= 1   } while( !stopLoop )

Referring to Table 11 above, a binary value X may be added to an end ofa bin string through each call of put(X). Herein, X may be 0 or 1.

In addition, for example, the limited EGk binarization process may beperformed as follows.

An input of the limited EGk binarization process may be a request forlimited EGk binarization, a rice parameter riceParam, log2TransformRange as a variable representing a binary logarithm of amaximum value, and maxPreExtLen as a variable representing a maximumprefix extension length. In addition, an output of the limited EGkbinarization process may be limited EGk binarization for symbolVal as avalue corresponding to an empty string.

A bit string of the limited EGk binarization process for the symbolValmay be derived as follows.

TABLE 12 codeValue = symbolVal >> riceParam PrefixExtensionLength = 0while( ( PrefixExtensionLength < maxPrefixExtensionLength ) &&     (codeValue > ( ( 2 << PrefixExtensionLength ) −2 ) ) ) {  PrefixExtensionLength++   put( 1 ) } if( PrefixExtensionLength = =maxPrefixExtensionLength )   escapeLength = 1og2TransformRange else {  escapeLength = PrefixExtensionLength + riceParam   put( 0 ) }symbolVal = symbolVal − ( ( ( 1 << PrefixExtensionLength ) − 1 ) <<riceParam ) while( ( escapeLength− − ) > 0 )   put( ( symbolVal >>escapeLength ) & 1 )

In addition, for example, the FL binarization process may be performedas follows.

An input of the FL binarization process may be a request for FLbinarization and cMax for the syntax element. In addition, an output ofthe FL binarization process may be FL binarization for symbolVal as avalue corresponding to a bin string.

FL binarization may be configured by using a bit string of which thenumber of bits has a fixed length of symbolVal. Herein, the fixed-lengthbit may be an unsigned integer bit string. That is, a bit string forsymbolVal as a symbol value may be derived through FL binarization, anda bit length (i.e., the number of bits) of the bit string may be a fixedlength.

For example, the fixed length may be derived as shown in the followingequation.

fixedLength=Ceil(Log 2(cMax+1))  [Equation 10]

Indexing of bins for FL binarization may be a method using a value whichincreases orderly from a most significant bit to a least significantbit. For example, a bin index related to the most significant bit may bebinIdx=0.

Meanwhile, for example, a binarization process for a syntax elementabs_remainder in the residual information may be performed as follows.

An input of the binarization process for the abs_remainder may be arequest for binarization of a syntax element abs_remainder[n], a colourcomponent cIdx, and a luma position (x0, y0). The luma position (x0, y0)may indicate a top-left sample of a current luma transform block basedon the top-left luma sample of a picture.

An output of the binarization process for the abs_remainder may bebinarization of the abs_remainder (i.e., a binarized bin string of theabs_remainder). Available bin strings for the abs_remainder may bederived through the binarization process.

A rice parameter cRiceParam for the abs_remainder[n] may be derivedthrough a rice parameter derivation process performed by inputting thecolor component cIdx and luma position (x0, y0), the current coefficientscan position (xC, yC), log 2TbWidth, which is the binary logarithm ofthe width of the transform block, and log 2TbHeight, which is the binarylogarithm of the height of the transform block. A detailed descriptionof the rice parameter derivation process will be described later.

In addition, for example, cMax for abs_remainder[n] to be currentlycoded may be derived based on the rice parameter cRiceParam. The cMaxmay be derived as shown in the following equation.

cMax=6<<cRiceParam  [Equation 11]

Meanwhile, binarization for the abs_remainder, that is, a bin string forthe abs_remainder, may be concatenation of a prefix bin string and asuffix bin string in the presence of the suffix bin string. In addition,in the absence of the suffix bin string, the bin string for theabs_remainder may be the prefix bin string.

For example, the prefix bin string may be derived as described below.

A prefix value prefixVal of the abs_remainder[n] may be derived as shownin the following equation.

prefixVal=Min(cMax,abs_remainder[n])  [Equation 12]

A prefix of the bin string (i.e., a prefix bin string) of theabs_remainder[n] may be derived through a TR binarization process forthe prefixVal, in which the cMax and the cRiceParam are used as aninput.

If the prefix bin string is identical to a bit string in which all bitsare 1 and a bit length is 6, a suffix bin string of the bin string ofthe abs_remainder[n] may exist, and may be derived as described below.

The rice parameter deriving process for the dec_abs_level[n] may be asfollows.

An input of the rice parameter deriving process may be a colourcomponent index cIdx, a luma position (x0, y0), a current coefficientscan position (xC, yC), log 2TbWidth as a binary logarithm of a width ofa transform block, and log 2TbHeight as a binary logarithm of a heightof the transform block. The luma position (x0, y0) may indicate atop-left sample of a current luma transform block based on a top-leftluma sample of a picture. In addition, an output of the rice parameterderiving process may be the rice parameter cRiceParam.

For example, a variable locSumAbs may be derived similarly to a pseudocode disclosed in the following table, based on an array AbsLevel[x][y]for a transform block having the given component index cIdx and thetop-left luma position (x0, y0).

TABLE 13 locSumAbs = 0 if( xC < (1 << log2TbWidth) − 1) {   locSumAbs +=AbsLevel[ xC +1 ][ yC ]   if( xC < (1 << log2TbWidth) − 2 )      locSumAbs += AbsLevel[ xC +2 ][ yC ]   if( yC < (1 <<log2TbHeight) − 1 )       locSumAbs += AbsLevel[ xC +1 ][ yC +1 ] (1532)} if( yC < (1 << log2TbHeight) − 1) {   locSumAbs += AbsLevel[ xC ][ yC+1 ]   if( yC <(1 << log2TbHeight) − 2 )       locSumAbs += AbsLevel[ xC][ yC + 2 ] } locSumAbs = Clip3( 0, 31, locSumAbs − baseLevel * 5 )

Then, based on the given variable locSumAbs, the rice parametercRiceParam may be derived as shown in the following table.

TABLE 14 locSumAbs 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 cRiceParam 0 00 0 0 0 0 1 1 1 1 1 1 1 2 2 locSumAbs 16 17 18 19 20 21 22 23 24 25 2627 28 29 30 31 cRiceParam 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3

Also, for example, in the rice parameter derivation process forabs_remainder[n], the baseLevel may be set to 4.

Alternatively, for example, the rice parameter cRiceParam may bedetermined based on whether a transform skip is applied to a currentblock. That is, if a transform is not applied to a current TB includinga current CG, in other words, if the transform skip is applied to thecurrent TB including the current CG, the rice parameter cRiceParam maybe derived to be 1.

Also, a suffix value suffixVal of the abs_remainder may be derived asshown in the following equation.

suffixVal=abs_remainder[n]cMax  [Equation 13]

A suffix bin string of the bin string of the abs_remainder may bederived through a limited EGk binarization process for the suffixVal inwhich k is set to cRiceParam+1, riceParam is set to cRiceParam, and log2TransformRange is set to 15, and maxPreExtLen is set to 11.

Meanwhile, for example, a binarization process for a syntax elementdec_abs_level in the residual information may be performed as follows.

An input of the binarization process for the dec_abs_level may be arequest for binarization of a syntax element dec_abs_level[n], a colourcomponent cIdx, a luma position (x0, y0), a current coefficient scanposition (xC, yC), log 2TbWidth as a binary logarithm of a width of atransform block, and log 2TbHeight as a binary logarithm of a height ofthe transform block. The luma position (x0, y0) may indicate a top-leftsample of a current luma transform block based on a top-left luma sampleof a picture.

An output of the binarization process for the dec_abs_level may bebinarization of the dec_abs_level (i.e., a binarized bin string of thedec_abs_level). Available bin strings for the dec_abs_level may bederived through the binarization process.

A rice parameter cRiceParam for dec_abs_level[n] may be derived througha rice parameter deriving process performed with an input of the colourcomponent cIdx, the luma position (x0, y0), the current coefficient scanposition (xC, yC), the log 2TbWidth as the binary logarithm of the widthof the transform block, and the log 2TbHeight as the binary logarithm ofthe height of the transform block. The rice parameter deriving processwill be described below in detail.

In addition, for example, cMax for the dec_abs_level[n] may be derivedbased on the rice parameter cRiceParam. The cMax may be derived as shownin the following table.

cMax=6<<cRiceParam  [Equation 14]

Meanwhile, binarization for the dec_abs_level[n], that is, a bin stringfor the dec_abs_level[n], may be concatenation of a prefix bin stringand a suffix bin string in the presence of the suffix bin string. Inaddition, in the absence of the suffix bin string, the bin string forthe dec_abs_level[n] may be the prefix bin string.

For example, the prefix bin string may be derived as described below.

A prefix value prefixVal of the dec_abs_level[n] may be derived as shownin the following equation.

prefixVal=Min(cMax,dec_abs_level[n])  [Equation 15]

A prefix of the bin string (i.e., a prefix bin string) of thedec_abs_level[n] may be derived through a TR binarization process forthe prefixVal, in which the cMax and the cRiceParam are used as aninput.

If the prefix bin string is identical to a bit string in which all bitsare 1 and a bit length is 6, a suffix bin string of the bin string ofthe dec_abs_level[n] may exist, and may be derived as described below.

The rice parameter deriving process for the dec_abs_level[n] may be asfollows.

An input of the rice parameter deriving process may be a colourcomponent index cIdx, a luma position (x0, y0), a current coefficientscan position (xC, yC), log 2TbWidth as a binary logarithm of a width ofa transform block, and log 2TbHeight as a binary logarithm of a heightof the transform block. The luma position (x0, y0) may indicate atop-left sample of a current luma transform block based on a top-leftluma sample of a picture. In addition, an output of the rice parameterderiving process may be the rice parameter cRiceParam.

For example, a variable locSumAbs may be derived similarly to a pseudocode disclosed in the following table, based on an array AbsLevel[x][y]for a transform block having the given component index cIdx and thetop-left luma position (x0, y0).

TABLE 15 locSumAbs = 0 if( xC < (1 << log2TbWidth) − 1 ) {   locSumAbs+= AbsLevel[ xC + 1 ][ yC ]   if( xC < (1 << log2TbWidth) − 2 )      locSumAbs += AbsLevel[ xC +2 ][ yC ]   if( yC < (1 <<log2TbHeight) − 1 )       locSumAbs += AbsLevel[ xC +1 ][ yC + 1 ](1532) } if( yC < (1 << log2TbHeight) − 1 ) {   locSumAbs += AbsLevel[xC ][ yC + 1 ]   if( yC < (1 << log2TbHeight) − 2 )       locSumAbs +=AbsLevel[ xC ][ yC + 2 ] } locSumAbs = Clip3( 0, 31, locSumAbs −baseLevel * 5 )

Then, based on the given variable locSumAbs, the rice parametercRiceParam may be derived as shown in the following table.

TABLE 16 locSumAbs 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 cRiceParam 0 00 0 0 0 0 1 1 1 1 1 1 1 2 2 locSumAbs 16 17 18 19 20 21 22 23 24 25 2627 28 29 30 31 cRiceParam 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3

Also, for example, in the rice parameter derivation process fordec_abs_level[n], the baseLevel may be set to 0, and the ZeroPos[n] maybe derived as follows.

ZeroPos[n]=(QState<2?1:2)<<cRiceParam  [Equation 16]

In addition, a suffix value suffixVal of the dec_abs_level[n] may bederived as shown in the following equation.

suffixVal=dec_abs_level[n]−cMax  [Equation 17]

A suffix bin string of the bin string of the dec_abs_level[n] may bederived through a limited EGk binarization process for the suffixVal inwhich k is set to cRiceParam+1, truncSuffixLen is set to 15, andmaxPreExtLen is set to 11.

Meanwhile, the RRC and the TSRC may have the following differences.

-   -   For example, in the TSRC, the Rice parameter for the syntax        element abs_remainder[ ] may be derived as 1. The rice parameter        cRiceParam of the syntax element abs_remainder[ ] in the RRC may        be derived based on the lastAbsRemainder and the lastRiceParam        as described above, but the rice parameter cRiceParam of the        syntax element abs_remainder[ ] in the TSRC may be derived as 1.        That is, for example, when transform skip is applied to the        current block (e.g., the current TB), the Rice parameter        cRiceParam for abs_remainder[ ] of the TSRC for the current        block may be derived as 1.    -   Also, for example, referring to Table 3 and Table 4, in the RRC,        abs_level_gtx_flag[n][0] and/or abs_level_gtx_flag[n][1] may be        signaled, but in the TSRC, abs_level_gtx_flag[n][0],        abs_level_gtx_flag[n][1], abs_level_gtx_flag[n][2],        abs_level_gtx_flag[n][3], and abs_level_gtx_flag[n][4] may be        signaled. Here, the abs_level_gtx_flag[n][0] may be expressed as        abs_level_gt1_flag or a first coefficient level flag, the        abs_level_gtx_flag[n][1] may be expressed as abs_level_gt3_flag        or a second coefficient level flag, the abs_level_gtx_flag[n][2]        may be expressed as abs_level_gt5_flag or a third coefficient        level flag, the abs_level_gtx_flag[n][3] may be expressed as        abs_level_gt7_flag or a fourth coefficient level flag, and the        abs_level_gtx_flag[n][4] may be expressed as abs_level_gt9_flag        or a fifth coefficient level flag. Specifically, the first        coefficient level flag may be a flag for whether a coefficient        level is greater than a first threshold (for example, 1), the        second coefficient level flag may be a flag for whether a        coefficient level is greater than a second threshold (for        example, 3), the third coefficient level flag may be a flag for        whether a coefficient level is greater than a third threshold        (for example, 5), the fourth coefficient level flag may be a        flag for whether a coefficient level is greater than a fourth        threshold (for example, 7), the fifth coefficient level flag may        be a flag for whether a coefficient level is greater than a        fifth threshold (for example, 9). As described above, in the        TSRC, compared to the RRC, abs_level_gtx_flag[n][0],        abs_level_gtx_flag[n][1], and abs_level_gtx_flag[n][2],        abs_level_gtx_flag[n][3], abs_level_gtx_flag[n][4] may be        further included.    -   Also, for example, in the RRC, the syntax element        coeff_sign_flag may be bypass coded, but in the TSRC, the syntax        element coeff_sign_flag may be bypass coded or context coded.

Meanwhile, in residual data coding of a block to which transform skip isapplied, that is, a transform skip block, in the case that syntaxelements are bypass-coded, the present disclosure proposes a method forcoding bypass-coded bins by grouping the bypass-coded bins for each ofthe syntax elements.

As a proposed embodiment, the number of context-coded bins available forresidual coding for a transform skip in one TU, that is, the TransformSkip Residual Coding (TSRC) described above, may be restricted to aspecific threshold value, and in the case that all context-coded binsavailable for the TU are consumed, and later, the syntax elements forthe TU are coded as bypass bins, a method is proposed for using a codingorder in which a syntax element is preferential instead of exitingcoding order in which a coefficient position is preferential.

Particularly, for example, in the conventional TSRC, coding of syntaxelements sig_coeff_flag, coeff_sign_flag, abs_level_gtx_flag[n] [0],par_level_flag, abs_level_gtx_flag[n] [1], abs_level_gtx_flag[n] [2],abs_level_gtx_flag[n] [3], abs_level_gtx_flag[n][4], and/orabs_remainder are included. The syntax elements described above may becoded in the order as shown in the following drawings.

FIG. 9 illustrates an example in which the syntax elements are coded inTSRC.

Meanwhile, in the present disclosure, a layer may mean a group/unit inwhich syntax elements are consecutively coded in a single repetitivestatement and may be described in the same meaning in the other elementsbelow. In addition, in FIG. 9, “sig” may represent sig_coeff_flag,“sign” may represent coeff_sign_flag, gt0 may representabs_level_gtx_flag[n] [0], “par” may represent par_level_flag, gt1 mayrepresent abs_level_gtx_flag[n] [1], gt2 may representabs_level_gtx_flag[n] [2], gt3 may represent abs_level_gtx_flag[n][3],gt4 may represent abs_level_gtx_flag[n][4], and “rem” may representabs_remainder.

For example, in the case of TSRC according to the present embodimentshown in FIG. 9, syntax elements may be coded in an order in whichpositions of the coefficients are preferential in a single layer. Thatis, for example, referring to FIG. 9, in the first layer,sig_coeff_flag, coeff_sign_flag, abs_level_gtx_flag[n][0], andpar_level_flag for a specific coefficient (e.g., Coeff₀) may be coded,and sig_coeff_flag, coeff_sign_flag, abs_level_gtx_flag[n][0], andpar_level_flag for the next coefficient (e.g., Coeff₁) may be coded.Later, for example, in the second layer, abs_level_gtx_flag[n] [1],abs_level_gtx_flag[n] [2], abs_level_gtx_flag[n] [3], andabs_level_gtx_flag[n] [4] for a specific coefficient (e.g., Coeff₀) maybe coded, and abs_level_gtx_flag[n][1], abs_level_gtx_flag[n] [2],abs_level_gtx_flag[n] [3], and abs_level_gtx_flag[n][4] for the nextcoefficient (e.g., Coeff₁) may be coded. Subsequently, in the thirdlayer, abs_remainder for all coefficients (e.g., from Coeff₀ toCoeff_(n-1)) in a subblock may be coded.

Meanwhile, in TSRC of VVC standard, as described above, the maximumnumber of available context-coded bins is restricted to a specificthreshold value (e.g., RemCcbs or MaxCcbs represented in Table 4) forresidual data coding, and the specific threshold value may be derivedbased on the number of samples included in a transform block or a widthand/or height of a transform block, and the like. For example, thespecific threshold value may be derived as represented in the equationbelow.

MaxCcbs=c×a horizontal side of a transform block×a vertical side of atransform block  [Equation 18]

Here, ‘c’ may represent an arbitrary real value. In the presentdisclosure, the c value is not limited to a specific value. For example,c may have an integer value such as 2 or a decimal value such as 1.5,1.75, or 1.25. In addition, for example, a threshold value to restrictthe maximum number of available context-coded bins may also be derivedbased on whether the transform block is a chroma block as well as thenumber of samples included in a transform block, and a width and/orheight of a transform block. In addition, the threshold value (RemCcbs)may be initialized in a unit of transform block, and the threshold valuemay be decreased as much as the number of context-coded bins used forcoding of the syntax element for residual data coding.

Meanwhile, in TSRC, syntax elements sig_coeff_flag, coeff_sign_flag,abs_level_gtx_flag[n] [0], par_level_flag, abs_level_gtx_flag[n] [1],abs_level_gtx_flag[n] [2], abs_level_gtx_flag[n] [3],abs_level_gtx_flag[n] [4], and/or abs_remainder may be context-coded butmay also be bypass-coded.

For example, ctxInc for the syntax elements described above may beallocated as represented in the following table.

TABLE 17 binIdx Syntax element 0 1 2 3 4 >=5 coded_sub_block_flag[ ][ ]0 . . . 7 (clause 9.3.4.2.6) na na na na na sig_coeff_flag[ ][ ] (MaxCcbs > 0) ? ( 0 . . . 93 na na na na na (clause 9.3.4.2.8) ) : bypasspar_level_flag[ ] ( MaxCcbs > 0) ? ( 0 . . . 32 na na na na na (clause9.3.4.2.9) ) : bypass abs_level_gtx_flag[ ] ( MaxCcbs > 0) ? (0.73 na nana na na (clause 9.3.4.2.9) ) bypass abs_remainder[ ] bypass bypassbypass bypass bypass bypass coeff_sign_flag[ ] bypass na na na na natransform_skip_flag[ x0 ][ y0 ] − − 0 coeff_sign_flag[ ] ( MaxCcbs +220) ? ( 0..5 na na na na na transform_skip_flag[ x0 ][ y0 ] = = 1 (clause9.3.4.2.10) ) : bypass

As represented in Table 17, in coding a syntax element sig_coeff_flag,coeff_sign_flag, abs_level_gtx_flag[n] [0], par_level_flag,abs_level_gtx_flag[n] [1], abs_level_gtx_flag[n] [2],abs_level_gtx_flag[n] [3], or abs_level_gtx_flag[n] [4], in the casethat a threshold value (e.g., RemCcbs or MaxCcbs) is greater than 0, thesyntax element may be coded as a context-coded bin, and in the case thata threshold value is less than or equal to 0, the syntax element may becoded as a bypass bin that uses a uniform probability distribution.

FIG. 10 illustrates another example in which the syntax elements arecoded in TSRC. For example, FIG. 10 may illustrate the case, aftercoeff_sign_flag for Coeff₀ is coded as a context-coded bin in coding anarbitrary sub-block/coefficient group in a transform block, a thresholdvalue becomes zero. In this case, referring to FIG. 10, the syntaxelements coded after the coeff_sign_flag for Coeff₀ includingabs_level_gtx_flag[n][0] for Coeff₀ may be coded as a bypass bin since aremaining threshold is zero, that is, there is no remainingcontext-coded bin available. The coding order of the embodiment shown inFIG. 9 described above may be maintained in the embodiment shown in FIG.10 without any change.

FIG. 11 illustrates another example in which the syntax elements arecoded in TSRC. In addition, for example, FIG. 11 may illustrate thecase, after abs_level_gtx_flag[n][2] for Coeff₀ is coded as acontext-coded bin in coding an arbitrary sub-block/coefficient group ina transform block, a threshold value becomes zero. In this case,referring to FIG. 11, the syntax elements coded after theabs_level_gtx_flag[n][2] for Coeff₀ including abs_level_gtx_flag[n] [3]for Coeff₀ may be coded as a bypass bin since a remaining threshold iszero, that is, there is no remaining context-coded bin available. Thecoding order of the embodiment shown in FIG. 9 described above may bemaintained in the embodiment shown in FIG. 11 without any change.

As described above, in the process of coding TSRC for a block in TSRC,in the case that all available remaining context-coded bins for theblock are used, the subsequent syntax element may be bypass-coded.However, in the conventional TSRC, in the case that all availableremaining context-coded bins are used and syntax elements are coded asbypass bins, as described above, the syntax elements may be coded in acoding order in which a coefficient position is preferential.Accordingly, the present disclosure proposes an embodiment ofbypass-coded coding syntax elements in a coding order in which a syntaxelement is preferential instead of the exiting coding order in which acoefficient position is preferential. Through this, the advantage of abypass coding engine having high throughput may be maximized, and theresidual data coding efficiency of an image may be improved.

Particularly, for example, the entropy encoder/entropy decoder mayinclude a binarization unit, a regular coding engine, and a bypasscoding engine. For example, a value of a syntax element may be input tothe binarization unit. The binarization unit may transform the value ofa syntax element to a bin string and output the bin string. Here, thebin string may mean a binary sequence or a binary code composed of oneor more bins. The bin may mean, when the value of a symbol and/or asyntax element is represented as a binary sequence (or binary code)through binarization, a value of each digit number (0 or 1) constitutingthe binary sequence (or binary code).

Later, the binarized signal (bin string) may be input to the regularcoding engine or the bypass coding engine. The regular coding engine mayallocate a context that reflects a probability value for a correspondingbin and code the corresponding bin based on the allocated context. Theregular coding engine may perform coding for each bin, and then, updatea probability and/or a context for the bin. The bins coded by using theregular coding engine may be referred to as a context-coded bin.

Furthermore, the bypass coding engine may bypass the process of updatingthe probability which was applied to the bin after processing ofestimating a probability for an input bin and coding the probability. Ina bypass mode, a context is not allocated according to an input bin, butan input bin is simply coded, and throughput may be improved. Forexample, in the bypass mode, a coding procedure may be performed byapplying a uniform probability distribution (0.5). The bins coded byusing the bypass coding engine may be referred to as a bypass-coded binor a bypass bin.

Generally, the bypass mode has better throughput performance than thecontext-coded bin. To code one context-coded bin, 1 or more than 1processing cycle may be required. However, for the bypass coding engine,only one cycle is required to code n bypass-coded bins. Here, n may begreater than 1. To improve throughput of entropy coding, it may bebeneficial to change a coding order (i.e., grouping) such thatbypass-coded bins are consecutively coded. Particularly, in the case ofgrouping bypass-coded bins, it may be beneficial to group thebypass-coded bins for each syntax element in the perspective ofthroughput and hardware complexity.

FIG. 12 illustrates an example of coding syntax elements bypass-coded inTSRC in a coding order in which a syntax element is preferential insteadof a coding order in which a coefficient position is preferential. Forexample, FIG. 12 may illustrate a case, after coeff_sign_flag for Coeff₀is coded as a context-coded bin in coding of an arbitrarysub-block/coefficient group in a transform block, a threshold valuebecomes zero. In this case, referring to FIG. 12, the syntax elementscoded after the coeff_sign_flag for Coeff₀ includingabs_level_gtx_flag[n][0] for Coeff₀ may be coded as a bypass bin since aremaining threshold is 0, that is, there is no remaining context-codedbin available. For example, referring to FIG. 12, the remaining contextelements (abs_level_gtx_flag[n][0] and par_level_flag) which arecontext-coded for Coeff₀ in the first layer may be bypass-codedaccording to the existing coding order, but later, the syntax elementsfor coefficients Coeff₁ to Coeff₁ may be coded in a syntax elementorder. In other words, later, sig_coeff_flags for coefficients Coeff₁ toCoeff_(n-1) may be bypass-coded consecutively, and subsequently,coeff_sign_flags for coefficients Coeff₁ to Coeff₁ may be bypass-codedconsecutively. Next, abs_level_gtx_flag[n][0]s for coefficients Coeff₁to Coeff₁ may be bypass-coded consecutively, and subsequently,par_level_flags for coefficients Coeff₁ to Coeff₁ may be bypass-codedconsecutively. In addition, for example, referring to FIG. 12, forcoding syntax elements in the subsequent layer after the first layer,the proposed coding order in which a syntax element is preferential maybe maintained.

FIG. 13 illustrates an example of coding syntax elements bypass-coded inTSRC in a coding order in which a syntax element is preferential insteadof a coding order in which a coefficient position is preferential. Forexample, FIG. 13 may illustrate a case, after abs_level_gtx_flag[n][2]for Coeff₀ is coded as context-coded bin in coding of an arbitrarysub-block/coefficient group in a transform block, a threshold valuebecomes zero. In this case, referring to FIG. 13, the syntax elementscoded after the abs_level_gtx_flag[n][2] for Coeff₀ includingabs_level_gtx_flag[n] [3] for Coeff₀ may be coded as a bypass bin sincea remaining threshold is 0, that is, there is no remaining context-codedbin available. For example, referring to FIG. 13, the remaining contextelements (abs_level_gtx_flag[n] [3] and abs_level_gtx_flag[n][4]) whichare context-coded for Coeff₀ in the second layer may be bypass-codedaccording to the existing coding order, but later, the syntax elementsfor coefficients Coeff₁ to Coeff_(n-1) may be coded in a syntax elementorder. In other words, later, abs_level_gtx_flag[n][1]s for coefficientsCoeff₁ to Coeff₁ may be bypass-coded consecutively, and subsequently,abs_level_gtx_flag[n][2]s for coefficients Coeff₁ to Coeff₁ may bebypass-coded. Consecutively. Next, abs_level_gtx_flag[n][3]s forcoefficients Coeff₁ to Coeff₁ may be bypass-coded consecutively, andsubsequently, abs_level_gtx_flag[n][4]s for coefficients Coeff₁ toCoeff₁ may be bypass-coded consecutively. In addition, for example,referring to FIG. 13, even for coding syntax elements in the subsequentlayer after the second layer, the proposed coding order preferential toa syntax element may be maintained.

Furthermore, the present disclosure proposes, in the case that syntaxelements are bypass-coded in a simplified residual data codingstructure, a method for coding bypass-coded bins by grouping thebypass-coded bins for each syntax element. Under a specific condition,there is an advantage in the coding performance perspective such aslossless coding or near-lossless coding, and the simplified residualcoding structure may be used for a single coding block or a transformblock. In this case, by using the method proposed in the presentdisclosure, instead of the existing coding order in which a coefficientposition is preferential, a coding order in which a syntax element ispreferential may be used.

In addition, since the number of context-coded bins usable for residualcoding in one TU may be restricted to a specific threshold value, in thecase that all context-coded bins usable for the TU are consumed andsubsequently, the syntax elements for the TU are coded as bypass bins,one embodiment in the present disclosure proposes a method for using acoding order in which a syntax element is preferential instead of theexisting coding order in which a coefficient position is preferential.Meanwhile, the existing simplified residual data coding structure may bethe same as those shown in the following drawings and the descriptionfor the drawing.

FIG. 14 illustrates an example in which syntax elements are coded in thesimplified residual data coding structure. Referring to FIG. 14, theexisting simplified residual data coding may include coding of syntaxelements sig_coeff_flag, coeff_sign_flag, and abs_remainder. FIG. 14 mayillustrate a syntax element coding order of the simplified residual datacoding structure having the existing coding order in which a coefficientposition is preferential for one subblock/coefficient group/transformblock/coding block.

For example, referring to FIG. 14, in the first layer, sig_coeff_flagand coeff_sign_flag for a specific coefficient may be coded,sig_coeff_flag and coeff_sign_flag for the next coefficient after thespecific coefficient may be coded, and sig_coeff_flag andcoeff_sign_flag for the coefficient up to the last coefficient positionon a scan order may be coded. Later, in the second layer, coding ofabs_remainder for all coefficients in a subblock may be performed in ascan order. Here, in the case that a value of the coefficient of theposition is zero, a value of sig_coeff_flag may be zero, and in the casethat a value of the coefficient of the position is non-zero, a value ofsig_coeff_flag may be 1. In addition, coeff_sign_flag may indicate asign of the coefficient of the position. For example, in the case thatthe coefficient of the position is zero, that is, in the case thatsig_coeff_flag for the coefficient is zero, coeff_sign_flag for thecoefficient may not be coded. Further, in the case that the coefficientis non-zero and a negative number, the coeff_sign_flag value for thecoefficient may be 1 (or zero), and in the case that the coefficient isnon-zero and a positive number, the coeff_sign_flag value for thecoefficient may be zero (or 1). Alternatively, in the case that thecoefficient is a negative number without regard to sig_coeff_flag forthe coefficient, the coeff_sign_flag value for the coefficient may be 1(or zero), and in the case that the coefficient is a positive number orzero, the coeff_sign_flag value for the coefficient may be zero (or 1).Alternatively, in the case that the coefficient is a positive numberwithout regard to sig_coeff_flag for the coefficient, thecoeff_sign_flag value for the coefficient may be 1 (or zero), and in thecase that the coefficient is a negative number or zero, thecoeff_sign_flag value for the coefficient may be zero (or 1).

Meanwhile, the present disclosure proposes a method for coding andgrouping for each syntax element to generate an advantage in CABACthroughput and hardware complexity in the simplified residual datacoding structure.

FIG. 15 illustrates an example of coding syntax elements bypass-coded inthe simplified residual data coding structure in a coding order in whicha syntax element is preferential instead of a coding order in which acoefficient position is preferential. For example, according to thepresent embodiment, as shown in FIG. 15, in the first layer, the bypasscoding may be consecutively performed from sig_coeff_flag of Coeff₀ tosig_coeff_flag of Coeff_(n-1), the last coefficient in a scan order, andsubsequently, consecutively performed from coeff_sign_flag of Coeff₀ tocoeff_sign_flag of Coeff_(n-1), the last coefficient in the scan order.Later, the bypass coding may be consecutively performed fromabs_remainder of Coeff₀ to abs_remainder of Coeff_(n-1), the lastcoefficient in the scan order.

Meanwhile, the simplified residual data coding structure may have asyntax structure different from that shown in FIG. 14 described above.For example, the simplified residual data coding structure as shown inthe following drawing may be coded.

FIGS. 16a and 16b illustrate embodiments in which syntax elements arecoded in the simplified residual data coding structure. Referring toFIGS. 16a and 16b , the simplified residual data coding may includecoding of syntax elements dec_abs_level and coeff_sign_flag. FIGS. 16aand 16b may illustrate a syntax element coding order of the simplifiedresidual data coding structure having the existing coding order in whicha coefficient position is preferential for one subblock/coefficientgroup/transform block/coding block. For example, referring to FIG. 16a ,in a layer, dec_abs_level and coeff_sign_flag for a specific coefficientmay be coded, dec_abs_level and coeff_sign_flag for the next coefficientafter the specific coefficient may be coded, and dec_abs_level andcoeff_sign_flag for the coefficient up to the last coefficient positionon a scan order may be coded. In addition, for example, referring toFIG. 16b , in a layer, coeff_sign_flag and dec_abs_level for a specificcoefficient may be coded, coeff_sign_flag and dec_abs_level for the nextcoefficient after the specific coefficient may be coded, andcoeff_sign_flag and dec_abs_level for the coefficient up to the lastcoefficient position on a scan order may be coded.

Here, in the case that a value of the coefficient of the position iszero, a value of dec_abs_level may be zero, and in the case that a valueof the coefficient of the position is non-zero, a value of dec_abs_levelmay be an absolute value of the coefficient. In addition,coeff_sign_flag may indicate a sign of the coefficient of the position.For example, in the case that the coefficient of the position is zero,that is, in the case that dec_abs_level for the coefficient is zero,coeff_sign_flag for the coefficient may not be coded. Further, in thecase that the coefficient is non-zero and a negative number, thecoeff_sign_flag value for the coefficient may be 1 (or zero), and in thecase that the coefficient is non-zero and a positive number, thecoeff_sign_flag value for the coefficient may be zero (or 1).Alternatively, in the case that the coefficient is a negative numberwithout regard to dec_abs_level for the coefficient, the coeff_sign_flagvalue for the coefficient may be 1 (or zero), and in the case that thecoefficient is a positive number or zero, the coeff_sign_flag value forthe coefficient may be zero (or 1). Alternatively, in the case that thecoefficient is a positive number without regard to dec_abs_level for thecoefficient, the coeff_sign_flag value for the coefficient may be 1 (orzero), and in the case that the coefficient is a negative number orzero, the coeff_sign_flag value for the coefficient may be zero (or 1).

Meanwhile, the simplified residual data coding structure may be used inthe case of satisfying a specific condition in the RRC or TSRC describedabove. For example, residual data may be coded in the simplifiedresidual data coding structure in the case that a current block islossless coded or near-lossless coded, or in the case that all availablecontext coded bins are consumed for a current block.

For example, the present disclosure proposes, in the case that allavailable context coded bins for the current block are consumed in theTSRC for a current block, a method for coding the syntax elements of acoefficient for the current block in the simplified residual data codingstructure.

Particularly, for example, syntax elements according to the TSRC for acurrent block may be parsed. In this case, the maximum number of contextcoded bins available for the current block may be derived, and in thecase that all the maximum number of context coded bins for the currentblock are used for coding the syntax elements for previous transformcoefficients of a current transform coefficient on a scanning order, thesyntax elements for the current transform coefficient and the subsequenttransform coefficients of the current transform coefficient on ascanning order may be coded in the simplified residual data codingstructure. Accordingly, the syntax elements for the current transformcoefficient and the subsequent transform coefficients of the currenttransform coefficient on a scanning order may include coefficient levelinformation and a sign flag for a transform coefficient. The decodingapparatus may derive the transform coefficient based on the syntaxelements for the transform coefficient coded in the simplified residualdata coding structure. For example, the coefficient level informationmay represent an absolute value of a coefficient level of the transformcoefficient. Furthermore, the sign flag may represent a sign of thecurrent transform coefficient. The decoding apparatus may derive acoefficient level of the transform coefficient based on the coefficientlevel information and derive a sign of the transform coefficient basedon the sign flag.

Meanwhile, to generate an advantage in CABAC throughput and hardwarecomplexity, the present disclosure proposes a method for coding andgrouping syntax elements bypass-coded in the simplified residual datacoding structure shown in FIG. 16 for each syntax element.

FIGS. 17a and 17b illustrate an example of coding syntax elementsbypass-coded in the simplified residual data coding structure in acoding order in which a syntax element is preferential instead of acoding order in which a coefficient position is preferential. Forexample, according to the present embodiment, as shown in FIG. 17a , ina layer, bypass coding may be consecutively performed from dec_abs_levelof Coeff₀ to dec_abs_level of Coeff_(n-1), the last coefficient in ascan order, and subsequently, consecutively performed fromcoeff_sign_flag of Coeff₀ to coeff_sign_flag of Coeff_(n-1), the lastcoefficient in the scan order. Alternatively, for example, according tothe present embodiment, as shown in FIG. 17b , in a layer, the bypasscoding may be consecutively performed from coeff_sign_flag of Coeff₀ tocoeff_sign_flag of Coeff_(n-1), the last coefficient in a scan order,and subsequently, consecutively performed from dec_abs_level of Coeff₀to dec_abs_level of Coeff_(n-1), the last coefficient in the scan order.According to the present embodiment, bypass-coded bins may be groupedfor each syntax element and consecutively coded, and an effect may begenerated such as throughput of entropy coding may be improved, andhardware complexity may be reduced.

Meanwhile, the simplified residual data coding structure may have asyntax structure different from those of shown in FIG. 14, FIG. 16a ,and FIG. 16b described above. For example, the simplified residual datacoding structure as shown in the following drawing may be coded.

FIG. 18 illustrates embodiments in which syntax elements are coded inthe simplified residual data coding structure. Referring to FIG. 18,simplified residual data coding may include coding of syntax elementssig_coeff_flag, coeff_sign_flag, abs_level_gtx_flag[n][0],par_level_flag, and abs_remainder. FIG. 18 may illustrate a syntaxelement coding order of the simplified residual data coding structurehaving the existing coding order in which a coefficient position ispreferential for one subblock/coefficient group/transform block/codingblock. For example, referring to FIG. 18, in the first layer,sig_coeff_flag, coeff_sign_flag, abs_level_gtx_flag[n][0], andpar_level_flag for a specific coefficient may be coded, sig_coeff_flag,coeff_sign_flag, abs_level_gtx_flag[n][0], and par_level_flag for thenext coefficient after the specific coefficient may be coded, andsig_coeff_flag, coeff_sign_flag, abs_level_gtx_flag[n][0], andpar_level_flag for the coefficient up to the last coefficient positionon a scan order may be coded. Later, in the second layer, coding ofabs_remainder for all coefficients in a subblock may be performed in ascan order.

Meanwhile, to generate an advantage in CABAC throughput and hardwarecomplexity, the present disclosure proposes a method for coding andgrouping syntax elements bypass-coded in the simplified residual datacoding structure shown in FIG. 18 for each syntax element.

FIG. 19 illustrates an example of coding syntax elements bypass-coded inthe simplified residual data coding structure in a coding order in whicha syntax element is preferential instead of a coding order in which acoefficient position is preferential. For example, according to thepresent embodiment, as shown in FIG. 19, in the first layer, the bypasscoding may be consecutively performed from sig_coeff_flag of Coeff₀ tosig_coeff_flag of Coeff_(n-1), the last coefficient in a scan order,subsequently, consecutively performed from coeff_sign_flag of Coeff₀ tocoeff_sign_flag of Coeff_(n-1), the last coefficient in the scan order,subsequently, consecutively performed from abs_level_gtx_flag[n][0] ofCoeff₀ to abs_level_gtx_flag[n][0] of Coeff_(n-1), the last coefficientin the scan order, and subsequently, consecutively performed frompar_level_flag of Coeff₀ to par_level_flag of Coeff_(n-1), the lastcoefficient in the scan order. Later, in the second layer, the bypasscoding may be consecutively performed from abs_remainder of Coeff₀ toabs_remainder of Coeff_(n-1), the last coefficient in the scan order.According to the present embodiment, bypass-coded bins may be groupedfor each syntax element and consecutively coded, and an effect may begenerated such as throughput of entropy coding may be improved, andhardware complexity may be reduced.

FIG. 20 briefly illustrates an image encoding method performed by anencoding apparatus according to the present disclosure. The methodproposed in FIG. 20 may be performed by the encoding apparatus disclosedin FIG. 2. Particularly, for example, step S2000 may be performed by theresidual processor of the encoding apparatus, and steps S2010 and S2020may be performed by the entropy encoder of the encoding apparatus. Inaddition, although it is not shown in the drawing, a process of derivinga prediction sample may be performed by the predictor of the encodingapparatus, a process of deriving a residual sample for the current blockbased on the original sample and the prediction sample for the currentblock may be performed by the subtractor of the encoding apparatus, anda process of deriving reconstructed samples for the current block basedon the residual samples and the prediction samples for the current blockmay be performed by the adder of the encoding apparatus.

The encoding apparatus derives residual samples for a current block(step S2000). For example, the encoding apparatus may determine whetheran inter prediction or an intra prediction is performed to the currentblock and determine a specific inter prediction mode or a specific intraprediction mode based on an RD cost. According to the determined mode,the encoding apparatus may derive prediction samples for the currentblock and may derive the residual samples through a subtraction betweenthe original samples and the prediction samples for the current block.

The encoding apparatus generates residual information for the residualsamples (step S2010).

For example, the encoding apparatus may derive transform coefficientsfor the current block based on the residual samples. For example, theencoding apparatus may determine whether a transform is applied to thecurrent block. That is, the encoding apparatus may determine whether atransform is applied to the residual samples of the current block. Theencoding apparatus may determine whether a transform is applied to thecurrent block considering a coding efficiency. For example, the encodingapparatus may determine that a transform is not applied to the currentblock. The block to which a transform is not applied may be referred toas a transform skip block. That is, for example, the current block maybe a transform skip block.

When a transform is not applied to the current block, that is, when atransform is not applied to the residual samples, the encoding apparatusmay derive the derived residual samples as the current transformcoefficients. In addition, when a transform is applied to the currentblock, that is, when a transform is applied to the residual samples, theencoding apparatus may derive the transform coefficients by performing atransform for the residual samples. The current block may include aplurality of subblocks or coefficient groups (CGs). In addition, a sizeof the subblock of the current block may be a 4×4 size or 2×2 size. Thatis, the subblock of the current block may include a maximum of 16non-zero transform coefficients or a maximum of 4 non-zero transformcoefficients.

Here, the current block may be a coding block (CB) or a transform block(TB). In addition, the transform coefficient may also be represented asa residual coefficient.

Later, for example, the encoding apparatus may generate and encode thesyntax elements of Transform Skip Residual Coding (TSRC) for thetransform coefficients of the current block.

For example, the encoding apparatus may generate and encode the syntaxelements for the first transform coefficient to the n-th transformcoefficient of the current block. The residual information of thecurrent block may include the syntax elements for the first transformcoefficient to the n-th transform coefficient of the current block.

For example, the residual information may include the syntax elementsfor the first transform coefficient to the n-th transform coefficient ofthe current block. Here, for example, the syntax elements may be syntaxelements according to a first residual data coding structure ofTransform Skip Residual Coding (TSRC). The syntax elements according tothe first residual data coding structure may include context-codedsyntax elements and/or bypass-coded syntax elements for the transformcoefficient. The syntax elements according to the first residual datacoding structure may include syntax elements such as sig_coeff_flag,coeff_sign_flag, abs_level_gt1_flag, par_level_flag, abs_level_gtX_flag,abs_remainder, and/or coeff_sign_flag.

For example, the context-coded syntax elements for the transformcoefficient may include a significant coefficient flag indicatingwhether the transform coefficient is a non-zero transform coefficient, asign flag indicating a sign for the transform coefficient, a firstcoefficient level flag for whether a coefficient level for the transformcoefficient is greater than a first threshold value, and/or a paritylevel flag for a parity of a coefficient level for the transformcoefficient. In addition, for example, the context-coded syntax elementsmay include a second coefficient level flag for whether a coefficientlevel for the transform coefficient is greater than a second thresholdvalue, a third coefficient level flag for whether a coefficient levelfor the transform coefficient is greater than a third threshold value, afourth coefficient level flag for whether a coefficient level for thetransform coefficient is greater than a fourth threshold value, and/or afifth coefficient level flag for whether a coefficient level for thetransform coefficient is greater than a fifth threshold value. Here, thesignificant coefficient flag may be sig_coeff_flag, the sign flag may beceff_sign_flag, the first coefficient level flag may beabs_level_gt1_flag, and the parity level flag may be par_level_flag.Furthermore, the second coefficient level flag may be abs_level_gt3_flagor abs_level_gtx_flag, the third coefficient level flag may beabs_level_gt5_flag or abs_level_gtx_flag, the fourth coefficient levelflag may be abs_level_gt7_flag or abs_level_gtx_flag, and the fifthcoefficient level flag may be abs_level_gt9_flag or abs_level_gtx_flag.

In addition, for example, the bypass-coded syntax elements for thetransform coefficient may include coefficient level information for avalue (or coefficient level) of the transform coefficient and/or a signflag indicating a sign for the transform coefficient. The coefficientlevel information may be abs_remainder and/or dec_abs_level, and thesign flag may be ceff_sign_flag.

Furthermore, the number of context-coded syntax elements for the firsttransform coefficient to the n-th transform coefficient may be the sameas the maximum number of context-coded bins of the current block. Thatis, for example, all the context-coded bins for the current block may beused as bins of the context-coded syntax elements for the firsttransform coefficient to the n-th transform coefficient. For example,the maximum number of context-coded bins of the current block may bederived based on a width and a height of the current block. For example,the maximum number of context-coded bins of the current block may bederived as a value of the number of samples of the current blockmultiplied by a specific value. Here, the number of samples may bederived as a value of multiplying a width and a height of the currentblock. In addition, the specific value may have an integer value such as2 or a decimal value such as 1.5, 1.75, or 1.25.

Meanwhile, for example, the syntax elements according to the firstresidual data coding structure may be coded in a coding order accordingto a coefficient position. The coding order according to a coefficientposition may be a scanning order of the transform coefficients. Forexample, the scanning order may be a raster scan order. For example, theraster scan order may represent the order of scanning sequentially froma top line downwardly and scanning from left to right in each line. Forexample, the syntax elements according to the first residual data codingstructure may be coded in an order from the syntax elements for thefirst transform coefficient to the syntax elements for the n-thtransform coefficient. In addition, for example, when the current blockincludes a plurality of subblocks or coefficient groups (CGs), theplurality of subblocks or coefficient groups may be coded in thescanning order, and the syntax elements for transform coefficients ineach subblock or the coefficient group may be coded in the scanningorder.

Meanwhile, for example, the residual information may include a transformskip flag for the current block. The transform skip flag may indicatewhether a transform is applied to the current block. That is, thetransform skip flag may indicate whether a transform is applied to thetransform coefficients of the current block. The syntax elementindicating the transform skip flag may be transform_skip_flag describedabove. For example, when a value of the transform skip flag is zero, thetransform skip flag may represent that a transform is not applied to thecurrent block, and when a value of the transform skip flag is 1, thetransform skip flag may represent that a transform is applied to thecurrent block. For example, when the current block is a transform skipblock, a value of the transform skip flag for the current block may be1.

In addition, for example, the encoding apparatus may generate and encodethe syntax elements for the n+1th transform coefficient to the lasttransform coefficient of the current block.

For example, the residual information may include the syntax elementsfor the n+1th transform coefficient to the last transform coefficient ofthe current block. Here, for example, the syntax element may be syntaxelements according to a second residual data coding structure ofTransform Skip Residual Coding (TSRC). The syntax elements according tothe second residual data coding structure may be referred to as thesyntax elements according to the simplified residual data codingstructure. For example, when all context-coded bins for the currentblock are used as bins of the context-coded syntax elements for thefirst transform coefficient to the n-th transform coefficient, that is,for example, when the number of context-coded syntax elements for thefirst transform coefficient to the n-th transform coefficient is equalto or greater than the maximum number of context-coded bins of thecurrent block, the encoding apparatus may generate and encode the syntaxelements for the n+1th transform coefficient to the last transformcoefficient of the current block, which are the syntax elementsaccording to the second residual data coding structure of TSRC.

For example, the syntax elements according to the second residual datacoding structure may include bypass-coded syntax elements for thetransform coefficient. For example, the syntax elements according to thesecond residual data coding structure may include coefficient levelinformation and a sign flag for the transform coefficient. For example,the syntax elements according to the second residual data codingstructure may include coefficient level information for an absolutevalue of a coefficient level of the transform coefficient and a signflag for a sign of the transform coefficient. The syntax elements forthe transform coefficient may be coded based on a bypass. That is, theresidual syntax elements for the transform coefficient may be codedbased on a uniform probability distribution. For example, thecoefficient level information may represent an absolute value of acoefficient level of the transform coefficient. In addition, the signflag may represent a sign of the transform coefficient. For example,when a value of the sign flag is zero, the sign flag may indicate that acoefficient level of the transform coefficient is a positive value, andwhen a value of the sign flag is 1, the sign flag may indicate that acoefficient level of the transform coefficient is a negative value. Thecoefficient level information may be abs_remainder described above, andthe sign flag may be coeff_sign_flag described above.

Meanwhile, for example, the syntax elements according to the secondresidual data coding structure may be coded in a coding order accordingto a coefficient position. The coding order according to a coefficientposition may be a scanning order of the transform coefficients. Forexample, the scanning order may be a raster scan order. For example, theraster scan order may represent the order of scanning sequentially froma top line downwardly and scanning from left to right in each line. Forexample, the syntax elements according to the second residual datacoding structure may be coded in an order from the syntax elements forthe n+1th transform coefficient to the last transform coefficient. Inaddition, for example, when the current block includes a plurality ofsubblocks or coefficient groups (CGs), the plurality of subblocks orcoefficient groups may be coded in the scanning order, and the syntaxelements for transform coefficients in each subblock or the coefficientgroup may be coded in the scanning order.

In addition, for example, the syntax elements according to the secondresidual data coding structure may be coded in a coding order accordingto a syntax element. That is, for example, the syntax elements accordingto the second residual data coding structure may be coded in a codingorder in which a syntax element is preferential. For example,coefficient level information for the n+1th transform coefficient to thelast transform coefficient may be coded, and thereafter, sign flags forthe n+1th transform coefficient to the last transform coefficient may becoded. Particularly, for example, the coefficient level information maybe coded in an order from the coefficient level information for then+1th transform coefficient to the coefficient level information for thelast transform coefficient, and later, the sign flags may be coded in anorder from the sign flag for the n+1th transform coefficient to the signflag for the last transform coefficient.

The encoding apparatus encodes image information including the residualinformation (step S2020). The encoding apparatus may encode the imageinformation including the residual information. For example, theresidual information may include the syntax elements according to thefirst residual data coding structure and the syntax elements accordingto the second residual data coding structure.

For example, the encoding apparatus may encode the image informationincluding the syntax elements according to the first residual datacoding structure and the syntax elements according to the secondresidual data coding structure. For example, the image information mayinclude residual information of the current block. For example, theencoding apparatus may encode the image information including theresidual information and output the image information in a bitstreamformat. The bitstream may be transmitted to the decoding apparatusthrough a network or a storage medium.

In addition, for example, the encoding apparatus may generate and encodeprediction information for the current block. The image information mayinclude the prediction information for the current block. The predictioninformation may include information for an inter prediction mode or anintra prediction mode performed in the current block. The decodingapparatus may perform an inter prediction or an intra prediction for thecurrent block based on the prediction information received through thebitstream and derive prediction samples of the current block.

Meanwhile, the bitstream may be transmitted to the decoding apparatusthrough over a network or a (digital) storage medium. Here, the networkmay include a broadcasting network and/or a communication network, andthe digital storage medium may include various storage media such asUSB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like.

FIG. 21 briefly illustrates an encoding apparatus for performing animage encoding method according to the present disclosure. The methodproposed in FIG. 21 may be performed by the encoding apparatus disclosedin FIG. 20. Particularly, for example, the residual processor of theencoding apparatus may perform step S2000 shown in FIG. 20, and theentropy encoder of the encoding apparatus may perform steps S2010 andS2020. In addition, although it is not shown in the drawing, a processof deriving a prediction sample may be performed by the predictor of theencoding apparatus, a process of deriving a residual sample for thecurrent block based on the original sample and the prediction sample forthe current block may be performed by the subtractor of the encodingapparatus, and a process of deriving reconstructed samples for thecurrent block based on the residual samples and the prediction samplesfor the current block may be performed by the adder of the encodingapparatus.

FIG. 22 briefly illustrates an image decoding method performed by adecoding apparatus according to the present disclosure. The methodproposed in FIG. 22 may be performed by the decoding apparatus disclosedin FIG. 3. Particularly, for example, step S2200 shown in FIG. 22 may beperformed by the entropy decoder of the decoding apparatus, step S2210shown in FIG. 22 may be performed by the residual processor of thedecoding apparatus, and step S2220 shown in FIG. 22 may be performed bythe adder of the decoding apparatus. In addition, although it is notshown in the drawing, a process of receiving prediction information forthe current block may be performed by the entropy decoder of thedecoding apparatus, and a process of deriving a prediction sample of thecurrent block may be performed by the predictor of the decodingapparatus.

The decoding apparatus obtains residual information a current block(step S2200). The decoding apparatus may obtain image informationincluding residual information for the current block through abitstream.

The residual information may include the syntax elements for a transformcoefficient of the current block. Here, the current block may be acoding block (CB) or a transform block (TB). In addition, the transformcoefficient may also be represented as a residual coefficient. Inaddition, the current block may be a transform skip block.

For example, the decoding apparatus may obtain the syntax elements forthe first transform coefficient to the n-th transform coefficient of thecurrent block. For example, the residual information may include thesyntax elements for the first transform coefficient to the n-thtransform coefficient of the current block. Here, for example, thesyntax elements may be syntax elements according to a first residualdata coding structure of Transform Skip Residual Coding (TSRC). Thesyntax elements according to the first residual data coding structuremay include context-coded syntax elements and/or bypass-coded syntaxelements for the transform coefficient. The syntax elements according tothe first residual data coding structure may include syntax elementssuch as sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag,par_level_flag, abs_level_gtX_flag, abs_remainder and/orcoeff_sign_flag.

For example, the context-coded syntax elements for the transformcoefficient may include a significant coefficient flag indicatingwhether the transform coefficient is a non-zero transform coefficient, asign flag indicating a sign for the transform coefficient, a firstcoefficient level flag for whether a coefficient level for the transformcoefficient is greater than a first threshold value, and/or a paritylevel flag for a parity of a coefficient level for the transformcoefficient. In addition, for example, the context-coded syntax elementsmay include a second coefficient level flag for whether a coefficientlevel for the transform coefficient is greater than a second thresholdvalue, a third coefficient level flag for whether a coefficient levelfor the transform coefficient is greater than a third threshold value, afourth coefficient level flag for whether a coefficient level for thetransform coefficient is greater than a fourth threshold value, and/or afifth coefficient level flag for whether a coefficient level for thetransform coefficient is greater than a fifth threshold value. Here, thesignificant coefficient flag may be sig_coeff_flag, the sign flag may beceff_sign_flag, the first coefficient level flag may beabs_level_gt1_flag, and the parity level flag may be par_level_flag.Furthermore, the second coefficient level flag may be abs_level_gt3_flagor abs_level_gtx_flag, the third coefficient level flag may beabs_level_gt5_flag or abs_level_gtx_flag, the fourth coefficient levelflag may be abs_level_gt7_flag or abs_level_gtx_flag, and the fifthcoefficient level flag may be abs_level_gt9_flag or abs_level_gtx_flag.

In addition, for example, the bypass-coded syntax elements for thetransform coefficient may include coefficient level information for avalue (or coefficient level) of the transform coefficient and/or a signflag indicating a sign for the transform coefficient. The coefficientlevel information may be abs_remainder and/or dec_abs_level, and thesign flag may be ceff_sign_flag.

Furthermore, the number of context-coded syntax elements for the firsttransform coefficient to the n-th transform coefficient may be the sameas the maximum number of context-coded bins of the current block. Thatis, for example, all the context-coded bins for the current block may beused as bins of the context-coded syntax elements for the firsttransform coefficient to the n-th transform coefficient. For example,the maximum number of context-coded bins of the current block may bederived based on a width and a height of the current block. For example,the maximum number of context-coded bins of the current block may bederived as a value of the number of samples of the current blockmultiplied by a specific value. Here, the number of samples may bederived as a value of multiplying a width and a height of the currentblock. In addition, the specific value may have an integer value such as2 or a decimal value such as 1.5, 1.75, or 1.25.

Meanwhile, for example, the syntax elements according to the firstresidual data coding structure may be coded in a coding order accordingto a coefficient position. The coding order according to a coefficientposition may be a scanning order of the transform coefficients. Forexample, the scanning order may be a raster scan order. For example, theraster scan order may represent the order of scanning sequentially froma top line downwardly and scanning from left to right in each line. Forexample, the syntax elements according to the first residual data codingstructure may be coded in an order from the syntax elements for thefirst transform coefficient to the syntax elements for the n-thtransform coefficient. In addition, for example, when the current blockincludes a plurality of subblocks or coefficient groups (CGs), theplurality of subblocks or coefficient groups may be coded in thescanning order, and the syntax elements for transform coefficients ineach subblock or the coefficient group may be coded in the scanningorder.

In addition, for example, the residual information may include atransform skip flag for the current block. The transform skip flag mayindicate whether a transform is applied to the current block. That is,the transform skip flag may indicate whether a transform is applied tothe transform coefficients of the current block. The syntax elementindicating the transform skip flag may be transform_skip_flag describedabove. For example, when a value of the transform skip flag is zero, thetransform skip flag may represent that a transform is not applied to thecurrent block, and when a value of the transform skip flag is 1, thetransform skip flag may represent that a transform is applied to thecurrent block. For example, when the current block is a transform skipblock, a value of the transform skip flag for the current block may be1.

In addition, for example, the decoding apparatus obtains syntax elementsfor the n+1th transform coefficient to the last transform coefficient ofthe current block. For example, the residual information may include thesyntax elements for the n+1th transform coefficient to the lasttransform coefficient of the current block. Here, for example, thesyntax element may be syntax elements according to a second residualdata coding structure of Transform Skip Residual Coding (TSRC). Thesyntax elements according to the second residual data coding structuremay be referred to as the syntax elements according to the simplifiedresidual data coding structure. For example, when context-coded bins forthe current block are all used as bins of the context-coded syntaxelements for the first transform coefficient to the n-th transformcoefficient, that is, for example, when the number of context-codedsyntax elements for the first transform coefficient to the n-thtransform coefficient is equal to or greater than the maximum number ofcontext-coded bins of the current block, the decoding apparatus mayobtain the syntax elements for the n+1th transform coefficient to thelast transform coefficient of the current block, which are the syntaxelements according to the second residual data coding structure of TSRC.

For example, the syntax elements according to the second residual datacoding structure may include bypass-coded syntax elements for thetransform coefficient. For example, the syntax elements according to thesecond residual data coding structure may include coefficient levelinformation and a sign flag for the transform coefficient. For example,the syntax elements according to the second residual data codingstructure may include coefficient level information for an absolutevalue of a coefficient level of the transform coefficient and a signflag for a sign of the transform coefficient. The syntax elements forthe transform coefficient may be coded based on a bypass. That is, theresidual syntax elements for the transform coefficient may be codedbased on a uniform probability distribution. For example, thecoefficient level information may represent an absolute value of acoefficient level of the transform coefficient. In addition, the signflag may represent a sign of the transform coefficient. For example,when a value of the sign flag is zero, the sign flag may indicate that acoefficient level of the transform coefficient is a positive value, andwhen a value of the sign flag is 1, the sign flag may indicate that acoefficient level of the transform coefficient is a negative value. Thecoefficient level information may be abs_remainder described above, andthe sign flag may be coeff_sign_flag described above.

Meanwhile, for example, the syntax elements according to the secondresidual data coding structure may be coded in a coding order accordingto a coefficient position. The coding order according to a coefficientposition may be a scanning order of the transform coefficients. Forexample, the scanning order may be a raster scan order. For example, theraster scan order may represent the order of scanning sequentially froma top line downwardly and scanning from left to right in each line. Forexample, the syntax elements according to the second residual datacoding structure may be coded in an order from the syntax elements forthe n+1th transform coefficient to the last transform coefficient. Inaddition, for example, when the current block includes a plurality ofsubblocks or coefficient groups (CGs), the plurality of subblocks orcoefficient groups may be coded in the scanning order, and the syntaxelements for transform coefficients in each subblock or the coefficientgroup may be coded in the scanning order.

In addition, for example, the syntax elements according to the secondresidual data coding structure may be coded in a coding order accordingto a syntax element. That is, for example, the syntax elements accordingto the second residual data coding structure may be coded in a codingorder in which a syntax element is preferential. For example,coefficient level information for the n+1th transform coefficient to thelast transform coefficient may be coded, and thereafter, sign flags forthe n+1th transform coefficient to the last transform coefficient may becoded. Particularly, for example, the coefficient level information maybe coded in an order from the coefficient level information for then+1th transform coefficient to the coefficient level information for thelast transform coefficient, and later, the sign flags may be coded in anorder from the sign flag for the n+1th transform coefficient to the signflag for the last transform coefficient.

The decoding apparatus derives residual samples of the current blockbased on the residual information (step S2210). The decoding apparatusmay derive the residual samples of the current block based on theresidual information.

For example, the decoding apparatus may derive transform coefficients ofthe current block based on the syntax elements according to the firstresidual data coding structure and the syntax elements according to thesecond residual data coding structure.

For example, the decoding apparatus may derive the first transformcoefficient to the n-th transform coefficient of the current block basedon the syntax elements according to the first residual data codingstructure.

In addition, for example, the decoding apparatus may derive the n+1thtransform coefficient to the last transform coefficient based on thesyntax elements according to the second residual data coding structure.For example, the coefficient level for the transform coefficient may bederived as a value represented by the coefficient level information, andthe sign of the transform coefficient may be derived as a signrepresented by the sign flag. In this case, for example, the transformcoefficient may be derived without performing level mapping.

Later, for example, the decoding apparatus may derive residual samplesof the current block based on the transform coefficients. In oneexample, when it is derived that a transform is not applied to thecurrent block based on the transform skip flag, that is, when a value ofthe transform skip flag is 1, the decoding apparatus may derive thetransform coefficients as derive the residual samples of the currentblock. Alternatively, for example, when it is derived that a transformis not applied to the current block based on the transform skip flag,that is, when a value of the transform skip flag is 1, the decodingapparatus may derive the residual samples of the current block bydequantizing the transform coefficients. Alternatively, for example,when it is derived that a transform is applied to the current blockbased on the transform skip flag, that is, when a value of the transformskip flag is zero, the decoding apparatus may derive the residualsamples of the current block by inverse-transforming the transformcoefficients. Alternatively, for example, when it is derived that atransform is applied to the current block based on the transform skipflag, that is, when a value of the transform skip flag is zero, thedecoding apparatus may derive the residual samples of the current blockby dequantizing the transform coefficients and inverse-transforming thedequantized transform coefficients.

The decoding apparatus generates a reconstructed picture based on theresidual samples (step S2220). For example, the decoding apparatus maygenerate reconstructed samples and/or the reconstructed picture based onthe residual samples. For example, the decoding apparatus may perform aninter prediction mode or an intra prediction mode for the current blockbased on the prediction information received through the bitstream andderive prediction samples and may generate the reconstructed samplesthrough an addition of the prediction sample and the residual samples.

Later, as occasion demands, in order to improve subjective/objectiveimage quality, the decoding apparatus may apply the in-loop filteringprocess such as deblocking filtering, SAO and/or ALF process to thereconstructed picture as described above.

FIG. 23 briefly illustrates a decoding apparatus for performing an imagedecoding method according to the present disclosure. The method proposedin FIG. 22 may be performed by the decoding apparatus disclosed in FIG.23. Particularly, for example, the entropy decoder of the decodingapparatus may perform step S2200 shown in FIG. 22, the residualprocessor of the decoding apparatus may perform step S2210 shown in FIG.22, and the adder of the decoding apparatus may perform step S2220 shownin FIG. 22. In addition, although it is not shown in the drawing, aprocess of receiving prediction information for the current block may beperformed by the entropy decoder of the decoding apparatus shown in FIG.23, and a process of deriving a prediction sample of the current blockmay be performed by the predictor of the decoding apparatus shown inFIG. 23.

According to the present disclosure described above, the efficiency ofresidual coding may be improved.

Furthermore, according to the present disclosure, when the maximumnumber of context-coded bins for a current block is consumed in TSRC,syntax elements according to a simplified residual data coding structuremay be signaled, and through this, the coding complexity of bypass-codedsyntax elements is reduced, and the overall residual coding efficiencymay be improved.

Furthermore, according to the present disclosure, as a coding order ofbypass-coded syntax elements, an order in which a syntax element ispreferential may be used, and through this, the coding efficiency of thebypass-coded syntax elements may be improved, and the overall residualcoding efficiency may be improved.

In the above-described embodiment, the methods are described based onthe flowchart having a series of steps or blocks. The present disclosureis not limited to the order of the above steps or blocks. Some steps orblocks may occur simultaneously or in a different order from other stepsor blocks as described above. Further, those skilled in the art willunderstand that the steps shown in the above flowchart are notexclusive, that further steps may be included, or that one or more stepsin the flowchart may be deleted without affecting the scope of thepresent disclosure.

The embodiments described in this specification may be performed bybeing implemented on a processor, a microprocessor, a controller or achip. For example, the functional units shown in each drawing may beperformed by being implemented on a computer, a processor, amicroprocessor, a controller or a chip. In this case, information forimplementation (e.g., information on instructions) or algorithm may bestored in a digital storage medium.

In addition, the decoding apparatus and the encoding apparatus to whichthe present disclosure is applied may be included in a multimediabroadcasting transmission/reception apparatus, a mobile communicationterminal, a home cinema video apparatus, a digital cinema videoapparatus, a surveillance camera, a video chatting apparatus, areal-time communication apparatus such as video communication, a mobilestreaming apparatus, a storage medium, a camcorder, a VoD serviceproviding apparatus, an Over the top (OTT) video apparatus, an Internetstreaming service providing apparatus, a three-dimensional (3D) videoapparatus, a teleconference video apparatus, a transportation userequipment (e.g., vehicle user equipment, an airplane user equipment, aship user equipment, etc.) and a medical video apparatus and may be usedto process video signals and data signals. For example, the Over the top(OTT) video apparatus may include a game console, a blue-ray player, aninternet access TV, a home theater system, a smart phone, a tablet PC, aDigital Video Recorder (DVR), and the like.

Furthermore, the processing method to which the present disclosure isapplied may be produced in the form of a program that is to be executedby a computer and may be stored in a computer-readable recording medium.Multimedia data having a data structure according to the presentdisclosure may also be stored in computer-readable recording media. Thecomputer-readable recording media include all types of storage devicesin which data readable by a computer system is stored. Thecomputer-readable recording media may include a BD, a Universal SerialBus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, a magnetic tape, afloppy disk, and an optical data storage device, for example.Furthermore, the computer-readable recording media includes mediaimplemented in the form of carrier waves (e.g., transmission through theInternet). In addition, a bit stream generated by the encoding methodmay be stored in a computer-readable recording medium or may betransmitted over wired/wireless communication networks.

In addition, the embodiments of the present disclosure may beimplemented with a computer program product according to program codes,and the program codes may be performed in a computer by the embodimentsof the present disclosure. The program codes may be stored on a carrierwhich is readable by a computer.

FIG. 21 illustrates a structural diagram of a contents streaming systemto which the present disclosure is applied.

The content streaming system to which the embodiment(s) of the presentdisclosure is applied may largely include an encoding server, astreaming server, a web server, a media storage, a user device, and amultimedia input device.

The encoding server compresses content input from multimedia inputdevices such as a smartphone, a camera, a camcorder, etc. Into digitaldata to generate a bitstream and transmit the bitstream to the streamingserver. As another example, when the multimedia input devices such assmartphones, cameras, camcorders, etc. directly generate a bitstream,the encoding server may be omitted.

The bitstream may be generated by an encoding method or a bitstreamgenerating method to which the embodiment(s) of the present disclosureis applied, and the streaming server may temporarily store the bitstreamin the process of transmitting or receiving the bitstream.

The streaming server transmits the multimedia data to the user devicebased on a user's request through the web server, and the web serverserves as a medium for informing the user of a service. When the userrequests a desired service from the web server, the web server deliversit to a streaming server, and the streaming server transmits multimediadata to the user. In this case, the content streaming system may includea separate control server. In this case, the control server serves tocontrol a command/response between devices in the content streamingsystem.

The streaming server may receive content from a media storage and/or anencoding server. For example, when the content is received from theencoding server, the content may be received in real time. In this case,in order to provide a smooth streaming service, the streaming server maystore the bitstream for a predetermined time.

Examples of the user device may include a mobile phone, a smartphone, alaptop computer, a digital broadcasting terminal, a personal digitalassistant (PDA), a portable multimedia player (PMP), navigation, a slatePC, tablet PCs, ultrabooks, wearable devices (ex. Smartwatches, smartglasses, head mounted displays), digital TVs, desktops computer, digitalsignage, and the like. Each server in the content streaming system maybe operated as a distributed server, in which case data received fromeach server may be distributed.

The claims described in the present disclosure may be combined invarious ways. For example, the technical features of the method claimsof the present disclosure may be combined to be implemented as anapparatus, and the technical features of the apparatus claims of thepresent disclosure may be combined to be implemented as a method. Inaddition, the technical features of the method claim of the presentdisclosure and the technical features of the apparatus claim may becombined to be implemented as an apparatus, and the technical featuresof the method claim of the present disclosure and the technical featuresof the apparatus claim may be combined to be implemented as a method.

1. An image decoding method, performed by a decoding apparatus, themethod comprising: obtaining residual information of a current block;deriving residual samples of the current block based on the residualinformation; and generating a reconstructed picture based on theresidual samples, wherein the obtaining the residual informationcomprises: obtaining syntax elements for a first transform coefficientto an n-th transform coefficient of the current block; and obtainingsyntax elements for an n+1th transform coefficient to a last transformcoefficient of the current block, wherein a number of context-codedsyntax elements for the first transform coefficient to the n-thtransform coefficient is equal to a maximum number of context coded binsof the current block, wherein the syntax elements for the firsttransform coefficient to the n-th transform coefficient are syntaxelements according to a first residual data coding structure ofTransform Skip Residual Coding (TSRC), wherein the syntax elements forthe n+1th transform coefficient to the last transform coefficient aresyntax elements according to a second residual data coding structure ofthe TSRC, and wherein the syntax elements according to the secondresidual data coding structure include coefficient level information anda sign flag for a transform coefficient.
 2. The image decoding method ofclaim 1, wherein the current block is a transform skip block, wherein atransform skip flag representing whether transform is applied to thecurrent block is obtained, and wherein a value of the transform skipflag for the current block is
 1. 3. The image decoding method of claim1, wherein the deriving the residual samples includes: derivingtransform coefficients of the current block based on the syntax elementsaccording to the first residual data coding structure and the syntaxelements according to the second residual data coding structure; andderiving the residual samples based on the transform coefficients. 4.The image decoding method of claim 1, wherein the context-coded syntaxelements among the syntax elements according to the first residual datacoding structure includes a significant coefficient flag for whether atransform coefficient is a non-zero transform coefficient, a sign flagfor a sign for the transform coefficient, a first coefficient level flagfor whether a coefficient level of the transform coefficient is greaterthan a first threshold value, and a parity level flag for a parity ofthe coefficient level for the transform coefficient.
 5. The imagedecoding method of claim 1, wherein the maximum number of thecontext-coded bins of the current block is derived based on a width anda height of the current block.
 6. The image decoding method of claim 1,wherein the n+1th transform coefficient to the last transformcoefficient are derived based on the syntax elements according to thesecond residual data coding structure.
 7. The image decoding method ofclaim 6, wherein a coefficient level of the transform coefficient isderived as a value represented by the coefficient level information forthe transform coefficient, and a sign of the transform coefficient isderived as a sign indicated by the sign flag.
 8. The image decodingmethod of claim 1, wherein the context-coded bins for the current blockare all used as bins of the context-coded syntax elements for the firsttransform coefficient to the n-th transform coefficient.
 9. An imageencoding method, performed by an encoding apparatus, the methodcomprising: deriving residual samples for a current block; generatingresidual information for the residual samples; and encoding imageinformation including the residual information, wherein the generatingthe residual information comprises: deriving transform coefficients forthe current block based on the residual samples; generating syntaxelements for a first transform coefficient to an n-th transformcoefficient of the current block; and generating syntax elements for ann+1th transform coefficient to a last transform coefficient of thecurrent block, wherein a number of context-coded syntax elements for thefirst transform coefficient to the n-th transform coefficient is equalto a maximum number of context coded bins of the current block, whereinthe syntax elements for the first transform coefficient to the n-thtransform coefficient are syntax elements according to a first residualdata coding structure of Transform Skip Residual Coding (TSRC), whereinthe syntax elements for the n+1th transform coefficient to the lasttransform coefficient are syntax elements according to a second residualdata coding structure of the TSRC, and wherein the syntax elementsaccording to the second residual data coding structure includecoefficient level information and a sign flag for a transformcoefficient.
 10. The image encoding method of claim 9, wherein themaximum number of the context-coded bins of the current block is derivedbased on a width and a height of the current block.
 11. The imageencoding method of claim 9, wherein the current block is a transformskip block, wherein the image information includes a transform skip flagrepresenting whether transform is applied to the current block, andwherein a value of the transform skip flag for the current block is 1.12. The image encoding method of claim 9, wherein the context-coded binsfor the current block are all used as bins of the context-coded syntaxelements for the first transform coefficient to the n-th transformcoefficient.
 13. The image encoding method of claim 9, wherein thecontext-coded syntax elements among the syntax elements according to thefirst residual data coding structure includes a significant coefficientflag for whether a transform coefficient is a non-zero transformcoefficient, a sign flag for a sign for the transform coefficient, afirst coefficient level flag for whether a coefficient level of thetransform coefficient is greater than a first threshold value, and aparity level flag for a parity of the coefficient level for thetransform coefficient.
 14. A non-transitory computer-readable storagemedium storing a bitstream generated by a method, the method comprising:deriving residual samples for a current block; generating residualinformation for the residual samples; encoding image informationincluding the residual information; and generating the bitstreamincluding the image information, wherein the generating the residualinformation comprises: deriving transform coefficients for the currentblock based on the residual samples; generating syntax elements for afirst transform coefficient to an n-th transform coefficient of thecurrent block; and generating syntax elements for an n+1th transformcoefficient to a last transform coefficient of the current block,wherein a number of context-coded syntax elements for the firsttransform coefficient to the n-th transform coefficient is equal to amaximum number of context coded bins of the current block, wherein thesyntax elements for the first transform coefficient to the n-thtransform coefficient are syntax elements according to a first residualdata coding structure of Transform Skip Residual Coding (TSRC), whereinthe syntax elements for the n+1th transform coefficient to the lasttransform coefficient are syntax elements according to a second residualdata coding structure of the TSRC, and wherein the syntax elementsaccording to the second residual data coding structure includecoefficient level information and a sign flag for a transformcoefficient.
 15. The computer-readable storage medium of claim 14,wherein the maximum number of the context-coded bins of the currentblock is derived based on a width and a height of the current block.